Visual Studio shortcut for "quick fix"
If your cursor is on the item that is underlined, you can use Ctrl + . to pop up the intellisence/suggestion context menu.
Alt + Shift + F10 does the trick.
Via @Rohit from Visual Studio keyboard shortcut to automatically add the needed using statement
The feature is called the "Smart Tag".
Default Keyboard Shortcut Schemes (ReSharper documentation)
Stack Overflow question How does one set Visual Studio 2010 keyboard shortcuts comfortably, especially when using ReSharper?
Stack Overflow question Visual Studio keyboard shortcut to automatically add the needed 'using' statement
They can usually be invoked via the keyboard using either:
- Ctrl+. (on a standard QWERTY keyboard)
- Alt+Shift+F10 (if you've not got Function Lock enabled)