You might want to take a look at my code generator. It creates n-Tier code based on your designs, but it does come with out-of-the-box code to generate standard n-Tier frameworks, or frameworks based on the Patterns In Action framework.
But this code generator generates an infrastructure that is scalable and easy to maintain, and you can create your own framework for future applications that you build. So it could be a good place to start if you want some examples on how to build a good n-Tier framework.
Did I mention it's free and you have access to all the source code? It uses the MyGenerationSoftware code generation tool for generating the code (which is also free).
Here are some videos so you can see what it is and what it does.
King Wilder, Dec 31, 2010