Hrmm...
I think all I really want is a bigger screen and an upgraded front-facing camera.
Things I wouldn't mind being upgraded (but don't particularly bother me at this current moment) would be Siri, battery, CPU, RAM, and storage.
I'd also like to see some sort of change to the design of the OS. I mean, yes, it works and it does what it has to, but it's been the same since 2007. I guess they sort of threw us a bone with the dropdown notifications window with two widgets... but, come on? I really have nothing in mind though aside from widgets and those are typically quite lame and unnecessary. So yeah, no idea what Apple could do.
Inductive charging with my Mac would be kind of cool too.
Don't really care about 4G (AT&T, at least) as it's not available in any of the cities/towns I frequent. So meh
My guess for the iPhone 5: New design, ~4in screen, 4G, 10mp camera, maybe an upgraded front-facing camera, underclocked A6, 1GB RAM (or at least 768MB?), same storage options (16/32/64), Siri 2.0, no NFC