TortoiseSVN - The coolest interface to (Sub)version control
Xversion - Super easy enterprise class version control.
SnailSVN - Similar to Tortoise SVN for Windows but integrated into Finder
AnkhSVN - AnkhSVN is a Subversion SourceControl Provider for Visual Studio.
Slik SVN - SlikSVN is a free subversion client for the command line.
kdeSVN - Comfortable graphical SVN client for linux.