TortoiseSVN - The coolest interface to (Sub)version control
SmartSVN - SmartSVN is a graphical client for the Open Source version control system Subversion (SVN).
Xversion - Super easy enterprise class version control.
VisualSVN - VisualSVN - Subversion plugin for Visual Studio
AnkhSVN - AnkhSVN is a Subversion SourceControl Provider for Visual Studio.
RapidSVN - CollabNet, Facilitating Collaborative Software Development