I’m not too big on bloating my Visual Studio with addons and whatnot, but there are a few tweaks here and there. My Visual Studio color scheme is a slightly tweaked version of the Desert Nights scheme by Thomas Restrepo. You can grab it for Visual Studio 2008 here.
I also use the awesome Sonic File Finder addon. It allows you to search for files in your solutions. Programming can be a frantic excercise in jumping between numerous code files and the solution explorer is a really poor way to do it. Most of the time you know what file you’re going for, so just hitting ctrl+, and typing a part of the file name saves you a bunch of time and sanity.
I also used to use the ApexSQL Edit for its superior performance and intellisense feature but it kinda got rendered obsolete after the release of Sql Server 2008 with its built-in intellisense. ApexSQL Diff, however, is a great tool to have in your belt. It does what you’d expect: compares database schemas and merges them. It performs surprisingly complicated merges without breaking a sweat. Both of the aforementioned applications by ApexSQL are of extremely high quality, they perform well and are stable as the negation of something not very stable. Highly recommended.