Today at Build 2012 it was announced that https://tfspreview.com has RTM'd as Team Foundation Service on https://tfs.visualstudio.com.
Up until now there has been no pricing information, which had been a barrier to some people I have spoken to as they did not want to started using something without knowing the future cost.
So to the really good news, as of now
- It is free for up to 5 users
- If you have an active MSDN subscription it is also free. So a team of any size can use it as long as they all have MSDN
The announcement said to look out for further price options next year.
Check the full details at Soma's blog