Quoted from Dr_of_Style:check out mrpinball.com, always new entrys, lots of options.
True, but the prices at Mr. Pinball tend to be higher than here on Pinside, plus it takes a few days for those ads to post so if a good deal is cross-listed there it will likely be posted by the time you see the ad. Still, a nice resource for getting some sense of what's available and establishing a (high end) price range for specific games.