I have Craigslist rss feeds set up for certain terms in Outlook. The moment someone posts equipment in any nearby area I get the update. I don't pull the trigger often, but I have snagged a couple of good deals. 4 cornies at $10 each, a 20# tank for $25, and a two-tap jockey box with cold plate and regulator for $25.
Edit: How could I forget, I also went all-grain with a deal on a brewers complete setup. That was a little pricier, but I got a ton of equipment and ingredients.