SQL Prompt from Red Gate has been absolutely indispensible in my day-to-day database development for its intellisense features when it comes to creating queries, stored procedures, etc. Having SQL Prompt and other Red Gate Tools, like SQL Refactor, is critical for doing real database work. I can't imagine not having code completion / intellisense as well as code formatting that I get from SQL Prompt. For those of you not getting the benefit of intellisense in SQL Server 2005 Management Studio, you will be happy to know that SQL Server 2008 Management Studio will have intellisense!!
Just like Visual Studio, as you are entering T-SQL into SQL Server Management Studio it will provide intelligent code completion - automatically filling out proper syntax and keywords, database objects, and variables. I am sure this will excite quite a few developers. Heck, I am excited for everyone and I have been enjoying intellisense for quite some time with Red Gate's SQL Prompt :)