Since asking about Asterisk back in July, I've found that openpbx (now named CallWeaver) seems to be the preferred fork:
http://www.callweaver.org/ http://www.voip-info.org/wiki/view/OpenPBX.org%20FAQ
There's an RPM for RC2 in Fedora Development (AKA Rawhide) but it hasn't been updated in awhile. (The latest upstream release is RC5.)