Visual Studio is such a massively big product that even after years of working with it I sometimes stumble upon a new/better way to do things or things I didn't even know were possible.
For instance-
Crtl + R, Ctrl + W to show white spaces. Essential for editing Python build scripts.
Under "HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\8.0\Text Editor"
Create a String called Guides with the value "RGB(255,0,0), 80" to have a red line at column 80 in the text editor.
What other hidden features have you stumbled upon?
Make a selection with ALT pressed - selects a square of text instead of whole lines.