Instamapper.com was a pretty cool solution (until the end of 2012). Nothing radically novel in concept, but it does pretty much just work and with most devices with a GPS.
It’s a little different from Google Latitude, which has a social aspect (your friends) but no history. Latitude is built into Google Maps Mobile 3.0, so everyone will have this on their phone in a few days. That’ll be weird fur sure.
Amazingly I downloaded this app this morning at 3.0.0, by the time I’d told a friend about it the release was 3.0.1, and the last person I told got 3.0.2. I guess Google is excited about this one.