Here's one for the "frequent travelers" among you. Priceline.com is a good resource that allows you to bid on hotel rooms. Unfortunately it's hard to know how much to bid, since hotel markets are pretty segmented (i.e. the market for hotel rooms in downtown Dallas doesn't tell you much about the hotel market in suburban Atlanta). I's a common problem in auctions where you don't see other bids--bid too high, and you waste money; bid too low, and you don't get to buy.
Here's a very cool solution: Bidding For Travel is a bulletin board where other travelers share their recent successful priceline bidding experience on Priceline. As a result, you have better information about the minimum price you should offer to get your room.
HT: Sound Money Tips