TortoiseSVN - The coolest interface to (Sub)version control
Mercurial SCM - Mercurial is a free, distributed source control management tool.
VisualSVN - VisualSVN - Subversion plugin for Visual Studio
Vault VCS - SourceGear Vault Pro is a version control and bug tracking solution for professional development teams. Vault Standard is for those who only want version control.
Xversion - Super easy enterprise class version control.
GitHub Desktop - GitHub Desktop is a seamless way to contribute to projects on GitHub and GitHub Enterprise.