All opensource projects need good documentation. That's not a small task ;-) but it's needed to get adoption.<p>Pick something interesting but hard to start/learn/understand and WRITE. This will sharpen your communication skills, which is crucial when explaining stuff to non-technical people (like your manager).<p>The installer / upgrade part of any project is also equally important; but it's better covered because it's part of the build process (the only exceptions is that you're selling enterprise software to a multi-million $$$ company: in that case your software must be as hard to install as posible in order to justify selling professional services).
If you don't have a GitHub account yet then get one and find projects that interest you ("explore").<p>This tool here helps you to stay on course by sending you emails regularly:<p><a href="http://www.codetriage.com" rel="nofollow">http://www.codetriage.com</a>
> ... Which opensource needs contributors badly?<p>All of them. You might be better off choosing an open-source project based on your interests and background rather than looking for a project that's particularly desperate.