fine mr. smartypants, try these ideas on for size:
-When activated, a large sphere appears where the person activated it, which reduces damage done to allies in the sphere, and drains enemie's energy when they are in the sphere. When R is pressed again, or its time limit runs out, it explodes dealing damage to anything within the sphere (yes, I completely ripped off this idea from Moakai in LoL. Sue me). Cons: Easily abused against cappers unless there is some sort of restriction on it.
- A similar idea is one where while activated within a medium radius around you, enemies take constant damage while they are within that area (inspired from Garen).
- Deploys a clone that just continues in the direction you were going in to fool enemies (not smart clone however). You gain stealth right away so the clone can seem like you, then you reappear. Clone lasts until it takes 30% damage of your full health, or after a time limit. (taken from Wukong, although defender's meltdown mod had something that was similar where a clone moved with you)
- When activated, you teleport to within 20 meters of an enemy (don't know how it chooses enemy; might be health, proximity, or some sort of user selection). (inspired by nocturne)
- When activated, along the ground a series of charges blast chasing after an enemy for certain range (taken from Nautilus).
- Short range teleportation (forwards and completely targetable as to where you teleport to, although I guess this is one is useless with the warp core) (kassadin)
- Artillery Strike. Self explanatory. Large range. Either launches just one large shell, a series of shells in a small area, or you teleport there and make an explosion around you when you do (gangplank, pantheon)
- Teleport to an ally in need (shen)
- You turn into a dragon and gain superpowers or something (Shyvana)
- Increased acceleration when enemies with low health (passive or active) (warwick)
- Not going to suggest any stuns/slows/disables. Those may work in LoL, but they just make someone way too vulnerable in this game
- Regenerative missiles that shoot where your aiming and do moderate damage (can hold up to 4, gain back a new one every 15sec)
- Makes a cage around you, trapping any enemies inside it along with you to duke it out until it disappears (3d version of Jarvan)
- energy at the cost of health (its just the opposite of the regen core)
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I can rip off ideas from LoL all day!

Although I must say while some of those would be completely pointless, I can see some of them being useful. I tried to pick things that applied the most. Also, they all would need low cds, so such ones like the artillery strike would just be too spammable, and many would have to be weakened. Plus, many of them are damage oriented, which can really screw up the game, as we have weapons for that. Again, just throwing out a zillion ideas, because one of them is bound to be good (Dragon, dragon, I hope its the dragon...)