These descriptions are for the ultimate ability unless specified otherwise. The goal is not to add a fourth level of the ultimate, but more focused for extra utility, but some ults would be too strong or have less room for improvement so I added a some non-ult effects.
It gives all purpose stats like trinity so it could not be the best substitute for AD or AP items.
The cooldown "reduction" is applied before CDR, just like when leveling up a skill.
Ahri Increase dash range by 50, increase each bolt base damage by 15, reduce cooldown by 15.
Akali Increase max charges to 4, reduce recharge time by 3 seconds, increase base damage by 10.
Alistar Increase duration by 1, reduce cost to 0, gain same amount of bonus AD as AP.
Amumu Increase Radius by 50, increase base damage by 50, decrease cooldown by 20, decrease cost by 50.
Anivia Decrease cost by 20, decrease cooldown by 2, decrease passive cooldown by 1 minute.
Annie Tibbers gain 60% attack speed and 20% movement speed.
Ashe Increase base damage by 50 and gets +0.8 bonus AD ratio.
Blitzcrank Reduce proc to once every 2.0 seconds, gain 50 mana regen.
Brand Increase bounces to 5, increase base damage by 30.
Caitlyn The bullet passes through the first intercepting target to a second target who takes 40% of the damage, the ultimate gets 20% armor penetration
Cassiopeia Decrease cooldown by 20, poisoned targets suffer 15% MR reduction.
Cho'Gath Increase max stacks to 8, increase health per stack by 10, reduce cooldown by 10.
Corki Increase max missiles to 10, change damage type to physical.
Darius Decrease cooldown by 15, Darius gains 5% movement speed, hemorrhage stacks lasts for 8 seconds.
Diana Increase base damage by 30, Moonfall apply Moonlight. +10% attack speed
Dr. Mundo Remove cost, increase restored health percentage by 5.
Draven Decrease damage reduction to 6%, hitting minions does not reduce the damage output, increase base damage by 50.
Evelynn Kills and assists reduce cooldown by 25, Reduce shadow walk detection radius by 50.
Ezreal Decrease cooldown by 15, hitting minions does not reduce the damage. Essence Flux and Arcane Shift reduce all of Ezreal's cooldowns by 0.5 seconds.
Fiddlesticks While Crowstorm is active fiddle gains 20% movement speed, reduce cooldown by 20.
Fiora Increase strikes to 6, reduce cooldown by 10, increase base damage by 25.
Fizz The primary target takes additional 80 (+0.15 AP) true damage.
Galio Increase channeling duration to 2.5, Galio is immune to cc while channeling, increase damage cap to 50%.
Gangplank Cannon Barrage gains a chance to deal 75% extra damage (per canon ball), the chance is equal to crit chance, Gangplank gains bonus 20% crit chance.
Garen If this ability is used to finish an enemy, it's cooldown is reduced by 70%.
Gragas Apply 35% movement slow for 2 seconds, Gragas gains 200 health.
Graves Targets suffer 15% armor reduction for 3 seconds, increase both base damage by 30.
Hecarim Gains (+0.7 bonus AD) ratio for the second portion of damage, reduce cooldown by 10.
Heimerdinger All abilities' cooldowns are reduced by 2 seconds and their mana costs by 15. Heimer gains 10 mana regen
Irelia Increase heal by 5% from both sources, increase base damage by 15, range by 100 and missle speed by 100
Janna Increase the diameter by 200 (no effect to knock back range), Janna receives 30% less damage while channeling
Jarvan IV Decrease cooldown by 10 seconds, knocks enemies other than the main target out of Cataclysm. (don't worry, you can still "help" your teammates.
Jax Jax's abilities stack his passive, his ult proc stacks it twice.
Jayce Movement speed buff duration increased to 2 seconds, decrease transformation cooldown by 2 seconds
Karma Max stacks of mantra becomes 3, on kills or assists she gains 1 stack.
Karthus Increase base damage by 30, decrease cooldown by 20, gains an 400 AoE damage centered around the targets but does damage the main target, the AoE magic damage is 40% of the main damage.
Kassadin Increase base damage by 60, decrease mana cost (base and per stack) by 40
Katarina For each blade hits an enemy increase the range by 15 (max 10 blades). Katarina's AA and abilities (ult excluded) that hit enemy champions reduce the cooldown of all her abilities by 0.3 second per champion hit.
Kayle Gives 40 Tenacity for 8 seconds and heals the target the same amount as Divine Blessing
Kennen Increase base damage by 10, each time an enemy champion gains a mark of the storm you restore 5 health and energy.
Kog'Maw Increase AD and AP ratio by 0.15 each.
LeBlanc Decrease cooldown by 3 seconds, LeBlance gains 15% movement speed for 3 seconds whenever she casts mimic.
Lee Sin You can cast R again to activate a resonating strike to the target, Extend flurry's effect to three strikes.
Leona Increase both CC duration by 0.5 seconds, increase passive's base damage by 15
Lulu Increase duration by 2 seconds, decrease cooldown by 10 seconds and gives 10% movement speed
Lux Decrease cooldown by 5, increase base damage by 30 and Illumination base damage by 50
Malphite Increase range by 150, AoE by 50, reduce cooldown by 10, when Granite Shield is active, Malphite gains 20 health regen
Malzahar The target takes 15% more damage during the duration from sources other than the ult
Maokai Reduce cost per second by 5, reduce cooldown by 5, allied units in the AoE instantly heal 20% of the total damage dealt to enemies
Master Yi Increase duration by 1, when highlander is not active kills and assists refresh half the amount (50% and 25%)
Miss Fortune Decrease cooldown by 15 seconds, increase cone width by 20% and range by 150.
Mordekaiser Target receives half healing effects during the duration. Iron Man max shield increased by 150 and Mordkaiser gains 5% spellvamp
Morgana Reduce cooldown by 10, gains 10% movement speed during the duration, Black shield absorb 50% of physical damage.
Nasus Decrease cooldown by 15, gains 20 armor and MR and 5% MS during the duration
Nautilus Decrease cooldown by 10 seconds, gains the ability to move through units and 10% MS for 3 seconds after activating the ability
Nidalee Gains 15 armor and MR in cougar form and +20 to base damage of all her abilities in cougar form.
Nocturne Increase range by 600, damage all units you pass through while traveling 70% of total damage.
Nunu Decrease channeling duration by 0.5 second, decrease cooldown by 10 seconds.
Olaf Increase duration by 2 seconds, Olaf gains 30% attack speed during the duration
Orianna Decrease cooldown by 10 seconds, increase base damage by 50.
Pantheon Increase AoE by 200, increase cast range by 1500. Pantheon gains 30% Movement speed for 2 seconds after the ult.
Poppy Increase duration by 1 second, the target takes 200 total magic damage over the duration and slowed by 5%
Rammus Decrease cooldown by 25 seconds, enemies hit by the tremors are slowed by 25% for 0.75 second.
Renekton Decrease cooldown by 20, gains 40 AD during the duration.
Rengar Increase duration by 1 second, increase bonus MS by 10%, Rengar gains 10% lifesteal.
Riven Increase duration by 2 seconds increase active base damage by 20.
Rumble Increase slow by 5%, decrease cooldown by 10 seconds, increase AoE by 80 (per missle)
Ryze Decrease cooldown by 20, increase duration by 2. (it is possible to keep it permenantly active with CDR and spamming)
Sejuani Frost and Permafrost apply 30% attack speed slow.
Shaco Before activating the ult, you gain 350 Max Health for the duration
Shen Decrease channeling time by 1 second, increase duration by 1 second, the targets gets 20% of Shen's armor and MR for the duration.
Shyvana Loses 5 fury per second instead of 6 while in dragon form, active gains +0.7 bonus AD ratio
Singed increase duration by 15, increase buff amount by 30, Singed gets feared once every 5 seconds for 0.5 second. (real insanity)
Sion Doubles his passive's chance and amount. +10% MS, +10% APen, +10% MPen.
Sivir Increase duration by 5 seconds, reduce cooldown by 20 seconds.
Skarner The second portion of the damage is applied in AoE and knocks back enemies from the main target. Range 450
Sona Decrease cooldown by 10 seconds, decrease power chord cost to 2 spells.
Soraka Astral Blessing and Wish apply 100 health regen to the targets for 5 seconds.
Swain Reduce upkeep cost by 2, gains 15 armor and MR while active.
Talon Increase duration by 1 second, Talon's AA reduce the cooldowns of all his abilities by 1.5 second except Noxian Diplomacy.
Taric Increase duration by 3 seconds, Taric gains 50 health and mana regen during the duration (half to allies)
Teemo Reduce cooldown by 7 seconds, increase max charges by 1
Tristana Reduce cooldown by 20, gains a +0.8 total AD ratio
Trundle Apply 10% slow during the duration, add +0.5 bonus AD ratio
Tryndamere Decrease cooldown by 15 seconds, the cooldown is further decreases by 1 second whenever Tryndamere critically strikes
Twisted Fate Increase range by 1000, reduce channeling time by 0.5 second, Stacked Deck becomes every third hit
Twitch Stealth duration gets doubled, Deadly Venom damage gets doubled.
Udyr Paste stance passive effect persists for 2 seconds after changing stances, monkey's agility gives Udyr 8 armor and MR per stack.
Urgot Increase range by 100, increase all Urgot's debuffs by 0.75 second (passive, W, E and ult)
Varus Decrease cooldown by 10, gains +0.7 bonus AD ratio.
Vayne Increase duration by 4 seconds, reduce cooldown by 15 seconds, gains additional 10 AD.
Veigar Decrease cooldown by 15 seconds, does 105% of opponent AP instead of 80%.
Viktor Decrease cooldown by 20 seconds, Hex Core give Viktor additional 3 Health, Mana and AP per level.
Vladimir Decrease cooldown by 10 seconds, increase damage amplification by 3%, Vladimir and allied units are healed for 130% of amplified damage they cause. edited idea from: Doc Tam
Volibear Decrease cooldown by 10 seconds, increase duration by 3 seconds, increase Frenzy's AS per stack by 5%.
Warwick Decrease mana cost by 50, strikes 6 times, increases total damage output by 20%.
Wukong Decrease cooldown by 10 seconds, increase AoE diameter by 80
Xerath Change cooldown to 1.5 seconds but can cast once, additional casts within 10 seconds costs a barrage stack (first does not cost a stack), Xerath gains a barrage stack every 15 seconds (Max 2)
Xin Zhao Increase the duration by 3 seconds, gains additional 20 armor and MR (not per champ) and 5% MS during the duration.
Yorick Decrease cooldown by 10 seconds, increase duration by 3 seconds (both), gives 150 extra health regen to the image (first one only).
Ziggs Decrease cooldown by 10 seconds, each time you use and ability decrease the cooldown by 2 seconds.
Zilean Decrease the mana costs of all abilities by 25, each time you use an ability you gain 8% CDR for 8 seconds(max 3 stacks).
Zyra Decrease cooldown by 10 seconds, Ult knocks enemies on edge back to the center a small distance (100), max seeds you can hold becomes 3, max on the field becomes 5, plants duration increases by 3 seconds.