I think I can summarize the majority of the future responses by saying "Find an itch you have that needs scratching and scratch it". In other words, find some job that you really wish you could automate or some nifty tool you wish you had or something of that nature and then do it.

Working on other peoples projects is rarely inspiring enough to persuade you to actually finish it, but if you really wanted to you could always browse the help wanted section on sourceforge.

One last note, there is actually a project somewhere around thats supposed to provide experience for semi-newbie perl programmers, the project is writing test cases for a bunch of modules on cpan but I don't have the link and can't find it, so hopefully somone will reply with the link.