Craigslist and ebay are your best bets, but you are going to have to be very lucky to get your asking price. The items you list can
be purchased new for little over $300.
For example, you can get 8GB of new
ram for $30 and you can get a quad core AMD CPU for $110 on Tiger Direct (I just checked). You'll probably have to reduce your asking price significantly
(personally, I think it should go for under $500) to sell it dude.