Not community, but there is http://cert.startcom.org/ .
You can also do your own (OpenSSL has everything you need).
And for a community one, you'd still need a verification mechanism and a protection mechanism for the roots; both of which could be hard to do in a volatile environment. http://www.cacert.org/ Seems to be that, don't think they are included in any browsers by default though (it's not in mine at least).
http://www.cacert.org/ has been jumping through Mozilla's hoops for years now, and no sign of being accepted. Shame, because they're certainly more secure than the typical "trusted" CA.
EDIT: Looks like CAcert withdrew their application until they get their internal audit out of the way: https://bugzilla.mozilla.org/show_bug.cgi?id=215243#c158
I wonder when or if we will get a chance to see a community signed and trusted SSL certificate provider.