A day after the first Gizmodo leak of the iPhone 4, I sold my 32GB iPhone 3GS, not-unlockable, for $550 in 1 day after posting it on CraigsList.
A week before the 2010 keynote, I sold my 16GB iPhone 3G, unlocked and jailbroken, for $300 in 90 minutes after posting it on CraigsList.
I'm prepping another 16GB iPhone 3G for sale after I get it cleaned up.
Coincidentally, I sold my Sony PlayStation 3 80GB fat model with a handful of games for $300 after 1 day and a half of posting.
CraigsList has never failed me. All were sold locally. I suggest including pictures, be very descriptive, and include immediate contact information (I used TextFree's SMS feature so not as to throw my cell phone number unnecessarily).
There's still a market out there and it moves damn fast.