Mother Jones launched an interactive map that shows US military presence around the world from 1950 to 2007. It's based on worldwide troop data from the Pentagon. From Mother Jones:
These numbers are often fuzzy: Some deployments are classified, others are temporary, and just because the Defense Department claims 30 US troops in Indonesia last year doesn't mean 1,500 didn't pass through on training missions. Even so, the map, and the associated research, should give you a good feel for what the Pentagon is up to around the world.
Mission Creep: US Military Presence Worldwide (Mother Jones)