Good open-source examples of properly tiered ASP.NET architectures.
clistctrl: My startup is using ASP.NET with C# I've decided to use the MVC framework.  Its quite phenomenal! Working with the MVC framework is more like working with ruby on rails but using C# instead of ruby, you don't get the heavy intermingling of layers that you inevitably will get with web forms + code behind.  In addition there is no more view state... in fact it is basically completely stateless.  Test driven development is also possible.  Right now its a free download.  I should also note how great it works with jQuery .