I love TripAdvisor; it's such a great resource. The peer reviews/rankings of hotels and attractions make travel planning simple!
The site also allow folks to create custom maps of places they've visited.
Note: on my map, I don't include places where I've only (a) visited the airport during a plane transfer (e.g. Dallas) or (b) driven through without stopping for anything more than taking a break (e.g. New Mexico, Texas, Utah, South Carolina, Virginia, Maryland, Delaware, Rhode Island and Kansas).