A lot of the registrars have services that let you register your interest in a domain name, and if the owner lets it expire, you get a shot at it. They're usually arranged as auctions, so that if more than one person wants it, you bid against each other. I tried it one time to see if I could get marsrovers.com, but it turned out somebody else wanted it badly enough to bid it up to near $300, so I dropped out at $100. Too rich for my blood.

GoDaddy's service is called "Domain Buy". When I check just now I noticed they're running a sale, and you might pick up the other "junk" variations of the name you want--.net, .biz, .us, etc.--for a couple of bucks each. Might be worth your while even if you have your heart set on the .com--that way you don't have to wait, and you build a fence around the .com, kinda like playing Go. When the teaser expires you'll still pay $8.95/each for yearly renewals, though. Caveat emptor.