I want to have a single controller and action.  I want them both to be by default so they don't clutter the URI.  To that end I have a route like this:

You could look at popping a Constraint onto the Route that says "id does not start with content/"

Constraints = new RouteValueDictionary(new { id = "<RegExp>" })

I'll let you work out the correct RegExp, I never was good at doing them off the top of my head.

I could find very little information on Constraints.  Any pointers?

This should work. 

routes.Add(new Route("{*id}", new MvcRouteHandler())
{
Defaults = new RouteValueDictionary(new { controller = "Album", action = "Index", id = "" }),
Constraints= new RouteValueDictionary(new { id = "^(?!Content).*" })
});

This route should match for any URL that does not start with Content. You might get caught if you have an album name that starts with Content, so maybe Content/ would work better in that expression.

See how it goes.

You don't need the ^ character. We take what you give us and wrap it like:

^(what-you-gave-us)$

 so your constraint on id could be changed to: id="(?!content).*"