I have a found using Beanstalk and Basecamp together to be absolutely awesome. It gives us the ability to use todos/milestones as well as establish polices (coding standards, design docs, etc) on Whiteboards.

The best part - and what gets the most use - is Messaging/comments. The ability to post comments directly related to a commit has become insanely powerful for our 2-man crew.

Best of all, you can do it all for free.