One place for looking up such information is the NetLantis GASP http://mogwai.frnog.org/sysctl/gasp/
It's not very accurate at the moment, but they say they're working on a more accurate database of their own.
Another, also rather inaccurate tool is Xtraceroute http://www.dtek.chalmers.se/~d3august/xt/
Nevertheless, nice eye candy for the desktop
Note that at best, such tools can roughly tell where on earth "autonomous systems" (providers, universities, etc) are located, as long as they don't spread all over the world. Some of them do so.