Bernardo Heynemann has put together the beginnings of what I'm sure will turn into a popular extension to Team Foundation Server.
Project BHAL merges Windows Workflow Foundation with TFS work item tracking to allow an organization to define a custom workflow tuned to their particular environment.
I have had requests for similar functionality, and I have written custom webservices to fire on certain WIT events. This approach is very attractive, because it allows for much more flexible configuration.
In a recent DotNetRocks episode, Joel Semeniuk was bemoaning the lack of exactly this sort of feature in the current version of TFS.
Good on ya', Bernardo! I hope I can contribute once I get my production process template deployed, and all the users happy.
++Alan