Code I've written has been from a two- or three-liner all the way to a 600-line monitoring script

To be truly experienced, you're going to have to work on your one-liner skills :)

More seriously, what are your interests? That's what will determine what is a good fit for you. Pick a subject and search for open source perl projects concerning it. Sourceforge is not the whole tamale.

If you are at a loss for a subject, perhaps look into The Phalanx Project. Plenty of work there for anyone.