Mixamo is a relatively new service for the animation community, offering a huge library of customizable motions that can be applied to your characters. One of the key things about Mixamo is that it will retarget the animations to your character on the server, so that the resulting animation that you get is directly catered to your specific character. You have an interactive preview of this on the Mixamo web service.
Below are some workflow demos provided by Mixamo. More information over at the Mixamo website.
3ds Max Workflow Tutorial for Mixamo
Unity Workflow Tutorial: Mixamo