Whereis

Very much like where except that it will search for any program and show you not only where the program itself is, but also where any source code and/or man pages related to that program are in the standard path:

samizdata# whereis time
time: /usr/bin/time /usr/share/man/man1/time.1.gz /usr/src/usr.bin/time
samizdata#

See also: where, which, whatis, apropos