I've seen a lot of lists of what the iPhone needs, but this MacWorld list most resembled my own: Macworld: First Look: iPhone fixes we want to see. I'd break the list into two parts: one part that's highly desirable and the other part that's so critical I can't buy the phone for fear Apple doesn't intend to address the problems. The latter list includes third party applications, tasks, work/home/family calendar management, search, cut and paste, etc. I could live with the crummy AT&T network and the lack of GPS if I had those features.
My experience with iPhoto and Aperture has taught me that Apple can take an incredibly long time to add features I consider critical, such as Library merge in iPhoto and date value edits in Aperture (neither exist). Given that experience, I can't buy the darned phone hoping Apple will fix the deal killers. I'm not Apple's target market, and won't necessarily listen to my concerns.