The find command is another tool for your toolbox. With find you aren't restricted to programs; you can search for any file you want, using a variety of search criteria. For example, to search for a file by the name of README, starting in /usr/share/doc:

$ find /usr/share/doc -name README
/usr/share/doc/ion-20010523/README
/usr/share/doc/bind-9.1.3-r6/dhcp-dynamic-dns-examples/README
/usr/share/doc/sane-1.0.5/README