In the OSS community, you're generally going to hear the following suggested - svn (Subversion), svk, darcs, or git. CVS used to be the standard, but it sucked. For most OSS projects, all four are perfectly good. Very few Perl projects are in darcs, but that's probably just cultural. Git is the new kid on the block and several people I respect are starting to migrate, thus prompting me to consider the migration myself. But, I still use SVK over Subversion and it works just fine.