TortoiseSVN - The coolest interface to (Sub)version control
kdeSVN - Comfortable graphical SVN client for linux.
VisualSVN - VisualSVN - Subversion plugin for Visual Studio
SmartSVN - SmartSVN is a graphical client for the Open Source version control system Subversion (SVN).
Slik SVN - SlikSVN is a free subversion client for the command line.
Xversion - Super easy enterprise class version control.