VisualSVN Server - Get an easy to use Subversion (SVN) server for Windows. It works out-of-the-box and is suitable both for small business and enterprises. Available for free!
TortoiseSVN - The coolest interface to (Sub)version control
uberSVN - Free, easy to implement UI for Subversion which includes:
SnailSVN - Similar to Tortoise SVN for Windows but integrated into Finder
VisualSVN - VisualSVN - Subversion plugin for Visual Studio
Xversion - Super easy enterprise class version control.