UPDATE: Google Code Search was shutdown so this fun doesn't apply anymore.
Mmkay, this tip is probably a gazillion years late but Google Code Search is a great resource for a budding developer. Heck, I'm a relatively seasoned developer and I use it.
It allows you to search public source code using a variety of methods. You can search for an exact string or a regex. You can search certain files, certain packages and certain languages.
For instance, today I was curious how to use the Perl API for writing a Pidgin plugin as their documentation is a tad sparce. A quick search looking for Purple::Find::buddy and I found a whole bunch of examples. You can also use it for silly things, like looking for quotes from "Hitchiker's Guide To The Galaxy."
It's official, Google now owns me. sigh