Most companies sticking the iPad2 have now started to reduce the price in order to clear their stocks before the new one is released. This is a similar trend that happens with all new Apple launches, especailly the first generation iPad.
According to the recommendation from another technology site technobuffalo, Gazelle.com is a site to check out. They pay for the postage and packaging and it is a simple paper work job, however the price is falling as wee speak, so be quick.
Dont forget, there is also Ebay a common option or other auction style sites. Dont be afraid to look around and test your luck. Even Facebook marketplace might be a good chance.
Let us know how YOU did!