24hr has a good classified section Lots of quality stuff.
The AK Files has a really good one also.
Lots of forums have a min post count requirement to use their classifieds.
Lots of them also limit the number of classifieds they can post in a year without being a paying member, or require you to be a paying member to use the classifieds. I usually do a search of a seller on here to see if they're just a classifieds clown or if they actually contribute some.
