Any how, I have also used Craigslist to do keyword research using the SEO Quake tip I gave a few days ago. Now you might try a few cities for a specific niche starter phrase or go wide open category by category in search of a niche or starting point. Does not matter. You can filter it down to 3 and 4 word phrases using the keyword density tool on SEO Quake then export it out and remove everything not relevant. Then run these through Micro Niche Finder or Market Samurai in bulk fashion and see what comes out the other end. With a good hour work, you should be able to find some good niches or phrases.
In addition to that tip, I have been experimenting with the Craigs list RSS feeds as well. They are in the bottom right corner of any page or search. I use the RSS Shortcode Wordpress plugin from Joost de Valk to make a few feeds from some big cities of a keyword phrase or product name search and then grab the feed and burn it with Feedburner. I then display that feed on pages of my niche website down at the bottom as aggregated Google food. Plus you are linking out in to a reputable site not using an affiliate link and adding to your surfers experience. Good for everyone. Get the picture? You can bury this in a tab using the Post Tabs plugin as well so the surfer has to dig to get to it, but the SERPS see it straight on. This works by category or search in Craigslist. Give it a try on a page or two and test it out. Pretty cool, huh?