MSDN Virtual Lab: Express: What’s New in SQL Server 2005
I hadn't read anything about the new PIVOT and UNPIVOT functionality, and by following up on that I discovered about the introduction of Common Table Expressions which look like a much more elegant way of temporarily storing data for use within stored procedures etc. This should give a lot more flexibility.
The other thing I knew about but hadn't seen examples of was the TRY...CATCH functionality. This is a great addition, but it is a shame that it doesn't work with user defined functions as well.