I stumbled across Scott Van Vliet's blog on weblogs.asp.net a little while ago. While he doesn't seem to post very often, he does have a couple of gems that are backed up with some solid code:
Page Template Framework for ASP.NET 1.1
Search Engine Safe Urls in ASP.NET
His page template framework allows you to specify user controls that should be added to your web forms. You can specify which controls are loaded by a page based on directory structure simply by creating a custom configuration file and inheriting from a base Page class. It's a common enough technique, but Scott's taken it one step further by creating the necessary configuration file plumbing.
In the CMS project I've been working on in my spare time, I've always kept the idea of Search Engine Safe (SES) URL's in the back of my mind. I'm currently using a URL re-writing technique on my personal site, but it's not nearly as simple to implement as Scott's solution seems to be. He seems to have found a way to convert URL's with multiple query string parameters into an SES URL, and then convert it back again, all without too much fiddling around. I can't wait to try it out.