Don't forget Perlmonks. CPAN modules that need a hand are a great place to help. Some other places that might inspire you if all of CPAN doesn't are Cool Uses For Perl, Code Catacombs, and Snippets Section. They hold many ideas and partial to nearly-complete implementations of those ideas. Many of the nodes say things such as, "I might just get around to polishing this up and putting on CPAN someday".