Microsoft KB article 937137 has a list of all the post SP2 builds for SQL Server 2005. The most current build is 3182, released on July 17. More importantly, build 3179 is supposed to have a fix for the TokenAndPermUserStore cache growth problem, which they describe like this:
"The TokenAndPermUserStore cache store may continue to grow steadily and decrease performance"
I recently posted about that problem here.