Visual Studio 2013 IntelliSense stops working for ASP.NET MVC5 Controllers

Close Visual Studio. Delete the <ProjectName>.v12.suo file. Reopen solution.

Tools > Options > Text Editor > C# > General

Make sure that "Auto List Members" is checked

Resetting my settings or importing previously exported, working settings, and restarting Visual Studio worked: Tools > Import and Export Settings... > Reset all settings.

EDIT: This keeps happening to me, surprisingly often in VS Express, and occasionally in VS Professional. One thing I noticed in Pro, is that it has happened after unexpected shut downs (when IT forces a reboot in the middle of the night). So it may be related to Visual Studio not closing correctly. The technique described above has worked every time.