Well, every iPhone user obviously wants something different, but besides a front facing camera, a higher quality rear camera, and an led flash, there is one feature that everybody really, REALLY wants.
From the 1st iPhone, to the 3G, everybody wanted 3G. From the 3G to the 3GS, there was no single killer feature, and the prevalence of people talking about wanting a compass, or a faster processor was next to nothing compared to the talk about wanting a front facing camera.
You say "I am willing to bed it's not even half of the posters here wants that." If that is true, is there/what is the one killer feature that everybody wants in the hardware of the next iPhone?
And to the posters above who speak of low res. sub-vga front facing cameras, I think you're missing where apple would head with this. AT&T, with their crappy network would NEVER want millions of front facing camera iPhones making video calls, whether it be two way or one. The network can't support it, and if it did, knowing AT&T, video call would come with a large premium per month.
If Apple put a front facing camera in the iPhone, it would interface with iChat. You would be able to video chat friends and family while connected to wifi only, not 3G. Mobile video chat, not video "calls" per se. While it might be a gimmick at first, it would be a step in the right direction. AFAIK, no us cell phone or carrier has the capability for two way video calls, but if Apple finds out that millions of people are utilizing video chat over wifi on their iPhones, a huge opportunity appears for AT&T to upgrade their infrastructure, and potentially see a huge profit margin from the fees that would be associated with it. It's a win-win-win. Win for the consumer, win for Apple, and an eventual win for wireless carriers.