I used AttributeRouting for a fairly large ASP.NET MVC 3 project. I found it really clean and useful - I preferred having the routing information declared on the methods themselves, rather than in some generic routing table, or a single catch-all route. With this library, you don't have to explicitly define a route on every method, there are convention-based approaches, and different levels at which you can define the base route, then more specific routes as you get closer to the methods themselves.

I also used T4MVC, which may have fallen by the wayside, but that kept a lot of the "magic strings" out of the code.

http://mvccontrib.codeplex.com/wikipage?title=T4MVC