Collapse all Visual Studio toolbox regions shortcut

While the focus is on the toolbox, press / to Collapse All.

You can also Expand All by pressing SHIFT+8

Here's an article by Sarah Ford with more information: Visual Studio Tip #186

BEFORE:

_{(source: msdn.com)}

AFTER:

_{(source: msdn.com)}

Shift + Alt + Enter is your friend.

Also see Window>Auto Hide All