We are a mostly MS shop at work doing .NET LOB development. We also use MS Dynamics for our CRM app... all the devs are currently using VS/SQL Server 2008. We also use VSS, but
This question has a lot of good answers about TeamCity. It does not compare to TFS but it might shed some light on TeamCity for you.
I have used both, and I have had success with both, but TeamCity was so much easier. TeamCity was a breeze to set up and configure. TFS was not. TeamCity is rock solid, it's easy to maintain and it just plain works. The developers at JetBrains have done a great job responding to the community. They get a release out every 6 to 8 months that adds real value. TFS is on a 2 year or more cycle.
TeamCity gives you more choice in how you build and what source control you use. It's not all in one, but that's sometimes a good thing. It's got a good set of extension points as well. We have also been really happy with the agent model it has.
I've gone through 3 absolutely painles upgrades in TeamCity. The one TFS upgrade we did took our build and source control down for 3 days. I'm the admin for TeamCity on our project and it takes up a couple of hours a month. TFS took a couple of days a week.
TeamCity + SVN + VisualSVN has been the smoothest environment I have ever worked in. TFS was generally smooth on the day to day, but only if someone was there keeping it running.
Hope that helps