If you spend time writing Stored Procedures or SQL Queries then SQL Prompt is a must have tool. It basically adds Intellisense for SQL Server and works well with SQL Server 2000 as well as SQL Server 2005.
The best news is that Red Gate is giving it away free of charge until the 1st of September.
Just to give you an example, I was just showing it off to one of my friends at work with a simple SELECT statement and he prompted me to write an INNER JOIN, lo and behold SQL Prompt looked up the foreign keys and went ahead and inserted the join clause linking the two fields between the tables.
Now this is a product that far exceeds the users expectations. Sweet!
Microsoft, shame on you for not including this in Developer Studio.