The HitMaps service provided a small world map showing where visitors to your site or blog live. They now started a new service called ClustrMaps™ (beta) which basically does the same. It's still free for smaller sites (< 1000 hits per day), but you'll have to pay if you run a more popular site.
(Wow, I just found out that I'm one of their TOP-50 users, though I'm far away from 1000 hits per day)
Users of the old HitMaps service can upgrade for free and get 5 invitations. New users are only accepted via such invitations at the moment.