I really enjoyed Shawn's presentation on Git Going with Git on Feb. 10th at the Surrey Drupal Users Group. We a record breaking turnout at 27 attendees with many coming all the way from downtown Vancouver.
Shawn demonstrated with a few simple commands how you can create a repository on your local computer and keep track of all your changes. Several team members can make changes and merge them together so that none of the changes are overwritten or lost.
You can store your code repository for free on github.com
but it's open to the public. Anyone can sign up for an account and download your code but that can only upload to your repository with your permission. For client work you can pay as little as $10.00 per month. You can also setup a Git repository on your web server and give access to your team members.
Git comes with a simple GUI but you can also download a Windows GUI client called TortoiseGit. It's enables you to right-click on a file or folder and add (commit) them to your repository.
For more information on Git: http://betterexplained.com/articles/a-visual-guide-to-version-control/