I sold two gen 1 iPhones on eBay several weeks ago. They were locked and used but in good shape, and both had v2.0 software. I listed them for $350 buy it now, and both sold in less than 12 hours. I think I could have gotten more, but didn't want to screw around with it.
I sold my 8gb last week on Craigslist in Phoenix for $450 jailbroke/unlocked. I had a lot of people inquire about it too. Sold it in two days. I had it replaced at the Apple Store due to some pixels going out, so it was in New condition when I sold it. Beats ebay since I didn't have to pay shipping or ebay fees.