Maybe I'm looking for a dependency visualizer/matrix. I'm not sure. I'm just trying to wrap my head around an existing and large web app, and I like pretty pictures. I know of Autodiagrammer but I don't think it would show the master page/subpage relationships. Is such a thing even possible?
If you are using Visual Studio 2010, you should be able to download a Feature Pack that should help you with what you are looking for. Additionally, here is a link for how you would do this ASP.NET projects using said Feature Pack.