A couple of weeks ago we had a Dev Lab on campus - during which time Michael Scherotter from MindJet was campus working with a few people from the TFS team who were showing him some of our Integration Features.
Mareen Philip forwarded a video to me of the end result - this is what Michael came up with after just four days - full integration with MindManager for requirements gathering synched up with TFS.
You can download the Mindjet Requirements Manager for TFS here and you can download a shockwave video demo here (video is also available inline on the page here)
Michael wrote a blog on his experiences here. It's well worth a look to see both the end results (a very cool extension to Mind Manager) as well as how much potential there is in integration with TFS.
What other ideas do you have for TFS integration solutions?