Earlier in the year I was getting upwards of $500 for it, but I saw in my town around 30 iPhones going up for sale. Some were 3G's and a lot were 3GS's going for mid 200's. I figured I needed to get it sold before the iPhone 4 came out because then I would take a real hit. I pretty much used a phone for 2 years and resold it for the same price I bought it at so I can't complain.
About ebay,
http://pages.ebay.com/help/sell/fees.html that's a list of their fees. Most notably, their final value fee, 9% of the ending sale price up to a max of $50. So the max fee of $5 is not true.