Smiley, go with Craigslist. The Boston Craigslist is pretty active. I got rid of loads of stuff in no time flat before I moved - though I was giving stuff away!
Price around the average SOLD price for comparable models on eBay, remembering that your buyer won't have to pay $40 or more for shipping. Whatever you do, don't overprice though - it will not sell. From a quick perusal of the completed items on eBay vs the prices listed on the G4 Tower Value Guide (for the Quicksilver 933 as an example) it would appear that they sell for somewhat LESS than the values given in the value guide, so do check.
If you're not an eBay member already, you will need to register in order to see the sold prices. (no charge for doing this) You cannot tell the sold prices from the active listings, as many things sell in the last few seconds of an auction.
Also, if you're new to eBay, it is usually good to build up at least a bit of reputation as a buyer before attempting to sell something - particularly a higher-priced item like a computer. When I, and most experienced eBayers go looking for something, sellers without established reputations are generally not people we want to send large amounts of money! Dealing face-to-face on Craigslist is different; as a buyer, I get to see and probably try out the item before parting with my money.
