Use slocate to build a database of files on your machine and use locate to find them:

# slocate -u # Rebuilds file database by scanning all filesystems
# locate foobar # finds all files with 'foobar' somewhere in the path

This is a particularly tasty utility that will tell you what a site is (and has been) running along with hosting and DNS lookup information. Just replace www.google.com with the URL of your choosing.

http://toolbar.netcraft.com/site_report?url=http://www.google.com/

Given an executable /path/to/EXEC:

$ ldd /path/to/EXEC