This application is pretty cool:
http://www.slate.com/features/mapthecandidates/It's a google maps-powered tool that shows you where all the candidates have campaigned every day from July 1st to the present, plus a news feed that gives you links to local papers about the candidate visits.
Today for example, it shows that Biden, Edwards, Richardson, Giuliani, and Romney are campaigning in IA. Romney also has an event in Columbus, OH. Huckabee's campaigning in NH. Paul's in DC. And McCain's in SC.
Looking at the full display of time from July 1 to today, you can see that Romney is the only one of the big 5 Republicans to have campaigned in NV (whereas all of the 4 leading Dems have done so). He's also the only one who's done much in MI outside of Detroit. And McCain's the only one of the 5 leading Republicans to have not been in FL since July 1. Anyway, it's fun to play with.