TortoiseGit is probably the best choice. It's low-friction, integrates well with Explorer and with PuTTY, and makes it painless to drop into the command line and invoke git manually when you need to.
In particular, TortoiseGit offers excellent UI for commit, revert, log/reflog, merging, and patch management. It also has some built in UI for Git-SVN if you use that.
The Windows GitHub client is shaping up nicely if you use GitHub but it's still in beta and super unstable.