www.moddb.com/forum

When you follow that link it will take you to the website that helped me get my sound design gigs.  All you have to do is register for free and then browse the pimpage/posing and recruitment forums for sound design "openings."  Please keep in mind that at least 90% of these guys work for free, and so should you (unless you end up working for an indie game company or something).  Also, here's a screenshot of the forum page that "highlights" the forums that you'll want to check out.

On a side note, I'm working on a couple mods right now and if you're interested in helping out or have any other questions, feel free to shoot me an e-mail at bgerstle@me.com

Hope this helps!