QuickSwitch

Works just like Ctrl+Tab. Press Ctrl+Alt+O to open the window. Hold Alt while pressing O to pick the file. Release Alt to select the file.

To change the shortcut, go to Tools -> Options -> Environment -> Keyboard and search for Tools.InvokeSwitchCommand. Make sure there are no conflicts with other commands or it won't work.

Some example use cases:

Switch between header and source files

Switch between XAML and code-behind

Switch between View and ViewModel