Ah, the iPhone. The person who has the iPhone -- and who never doesn't have the iPhone -- only needs one gift. But surely there's more than one to recommend.
You can't go wrong with this. You're basically giving the person cash, but you're narrowing down the possible uses of that cash to the stuff on iTunes -- books, movies, music, comics, video games -- all the nonsense a person can choose from. You are sending the message that you want them to spend their gifted spacebucks on a bunch of somethings that will be fun. $20-$100.
Drop 7 is the ultimate quick-play iOS game that you can also suggest is educational... as much as adding the digits 1-7 is educational. Tiny Tower teaches, uh, building management. Contre Jour will make them appreciate art. Scan through our year's worth of Gaming Apps of the Day. Most of them are for iPhone; plenty are worth considering. Free-$3.
They make it look like your iPhone is just your ear (or someone else's!) Do you need to be told that this would serve as a joke gift? $US20.
This solar-powered iPhone charging tree is expensive, artsy, French and possibly not on sale. They sold through their first batch, but keep an eye on their blog to see if they're taking more orders. Surely every dorm room needs one of these. And surely it'd never get broken or rained on with beer. $US370.