Releases are first made through SourceForge and can be found here. For each version there is a source release and binary releases for Linux, Windows, Solaris, and Darwin (includes OS X).
RPMs can be found on Planet CCRMA and rpmfind.net.
Debian packages can be found here.
Mac OS X users, be sure to check out MacFLAC, a FLAC distribution specifically for OS X, including a .pkg installer and applescript droplets. Or, if you use Fink, you can try the FLAC Fink package.
You can also get the nightly CVS tarball here.