I gave a presentation at TechEd 2008 where I covered our new features in "A Day in the Life of a DBA". Here's more of what I showed for 1:00pm - "New and Shiny":
With the stored procedure I created ready to go, I need to test it - in case it's long or complicated, or even spins off to another procedure, we now have the Transact-SQl (T-SQL) Debugger feature. This is something Microsoft put back in to SQL Server after having it years ago - but this time it's integrated right into SQL Server Management Studio (SSMS). All you have to do is bring up a procedure or set of statements, and then click the little green right-arrow in the toolbar or click "Debug" in the menu bar.
When you do, you're dropped into debug mode, and you can click the "Step Into", "Step Over" and so on buttons in the toolbar. You'll walk step-by step through the statements, and down below you'll get a list of the variables and their assignments. Priceless.