[Edit] I am looking primarily for personal work.
Long answer: It depends on what you're going to do with it. Are you looking for yourself, for personal work? Are you looking for multiple team members? Distributed? Centralized with no administrator? Centralized with an IT and administration team? Does the server have to be Windows? Does it have to support other OSes later? Does it have to integrate with a particular IDE on Windows? What about a hosted solution?
Companies with Windows development environments which I've worked at have used Subversion (and Trac) and Perforce, and I've heard of people using Microsoft SourceSafe (apparently deprecated in favor of Visual Studio Application Lifecycle Management) and SourceGear Vault. Bazaar (bzr) and Mercurial (hg) also should have decent Windows support.
As an aside, I've used Subversion (SVN) extensively on Windows with success as well. And Mercurial a bit too.
In all honesty, use a system that's intended to work on multiple platforms and trusted by thousands of others. You have plenty of choices, and most of the good ones will work well on Windows too, even if they were written with *nix/bsd systems in mind at first.
(go with git!) ;)
http://www.visualsvn.com/ for the server (there is a free version).
plus http://tortoisesvn.tigris.org/ for the client.
It works very well for all of my personal project and doesn't really require too much setup. I also have openSSH installed to make it a little more secure.
This also comes in handy because I can tunnel through it when I'm on an open wireless connection and all my web traffic is encrypted (even DNS requests).