I have used Craigslist for alot of sales. Chris is right, there are ALOT of scammers and junk mail saying "I am interested, click on this link."
I have used Ebay but they charge fees. Ebay is a great way to reach alot of people. I usually don't sell it directly on Ebay but I have found buyers and we agreed to price via email and then I canceled my auction (without a high bidder of course).
Also try www.boattrader.com but they charge as well.
Third vote for craigslist. It attracts scammers, but those are pretty easy to sniff out. More importantly, you're reaching out to a local audience. Helps with large items that can't be shipped (like a boat!). Sold my PT175 that way.
Of course this site! And Craigslist, Bassboatcentral.com, any local fishing/boating boards, also when I sold the Tracker i did paper a brochure with my phone number as tear offs (the old school way). I got a LOT of traffic from posting the brochures in each of the local gas stations, and tackle shops.