Here's a handy trick from Wired to use with craigslist.
If you just search craigslist, prepare to get aced out of some great apartments, torchiere lamps, and big-boned, er, companions. Check it: Every craigslist query is XML-enabled, which means it can power an RSS feed. And if you enter search parameters for, say, a beige 1982 Camaro for less than $500 (still a rip-off), the resulting Web address will be the same every time. Click the RSS button on the bottom right of the page. Use this to your junk-hunting advantage by pasting the URL into your RSS reader, so any new post that meets your criteria will show up there instantly.