All source code and binaries are distributed under open-source licenses. The libraries are distributed under the LGPL, and the plugins and command-line utilites (flac and metaflac) are distributed under the GPL. If you would like to redistribute parts or all of FLAC under different terms, contact me.
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.