ASP.NET 2.0 Themes/Skins
I've been doing a fair bit of work with ASP.NET 2.0 Themes the past day or two, and I have to say I'm impressed with it. If you haven't heard about ASP.NET themes yet, they are a nifty new feature in ASP.NET 2 that allows you to quickly create a Skin/Theme structure for your web interface. You can skin the controls that ship with ASP.NET and your own custom controls. Skins can programmatic-ally be set on an application and global level, which is great for an application where the user selects their theme. We took a set of themes we had done for an application and dropped them into our ASP.NET theme folders and within about 10 minutues had it hooked into the application, very cool.
For a good starter tutorial on it check out this one written by Bill Evjen.