This is a quick and possibly dirty way of getting selectable themes with MVC. This could be expanded to be used with profiles or post logon events.It is a good starter. Also I'm sure this could be done entirely in JQuery but getting the info to the controllers might be handy under some circumstances.
Add Selection on Session on the _layout.cshtml or masterpage
Then we need a dropdown (select) and some JQuery to select it.
Then we have the controller code which saves the session variable
OK you could have done all this with JQuery as discussed before, but putting stuff to and fro between MVC and html is fairly interesting and as I said opens the usage for saving this to a database and user profile.