That's exactly what List-Alert.com does. We send you an email when someone posts the thing you're looking for on Craigslist.
How does it work you might ask?
Craigslist provides an RSS feed that gives information for each of their postings. About once an hour, we check this RSS feed to see if the things you're looking for have been posted. When we get a hit, we send you an email to let you know.
Anyway, I hope you find it as useful as we do.
Thanks for giving it a try,
Ted (programmer, creator) and John (business guy extraordinaire, co-creator)
