Recently, I've started experimenting with the capabilities of add-ins for VS 2005 because I want to write some extensions for Team Foundation Server. However, before I could really get to work on the more complex add-ins I needed to start with something simple.
For anyone who has ever worked with Visual Studio 2005 solutions that contains multiple projects, you've probably spent a fair amount of time collapsing the project items in the Solution Explorer. So, my first "useful" add-in simply allows you to collapse all solution project items with a single mouse click.
After you install this add-in and run Visual Studio 2005, you will notice a new menu item, "Collapse All", when you right-click on a solution in the Solution Explorer. Selecting this menu option will collapse all project items within the solution.
I'm also planning on adding a few more features to this particular add-in down the road but even in its current state, it's already proven to be a time saver.
You can download the add-in here.