I Know that Sql SErver 2008 have a lot of new feature in Database Engine, but one of the most loved feature is intellisense in Management Studio. Intellisense really helps you to improve productivity when you write T-Sql code, and it is great to have it included in base version of the MS. The disappointing stuff is that it does not work when you connect to a sql server 2005 instance. In my opinion this is bad, but MS have its reason to do so.
In the meanwhile you can still buy a license for SQL prompt and use intellisense even in your Sql server 2005 management studio :P