Check out Pooln, a nifty web-2.0-y tool that uses a “community/social-network approach to carpooling.” You plug in your home zip code and your work zip code and it tries to find you someone to carpool with — it even has RSS feeds for zip codes, in case a new carpooler shows up. The future is now!
There’s a decent interview with the proprietor of Pooln on eHub.