Application Architecture Guide v 2.0 (beta 1)
I really like the Microsoft Patterns & Practices team with their guides (whole books, free to download) on how to build software solutions in a proper way.
Recently (couple of days ago) they have published a new version (2.0) of the Application Architecture Guide. It is a must for all architects, development leads or SD project leads, since it covers all architectural approaches you might to use in your solutions.
It will take some time to get through all the data in the guide so you can expect a couple of more dedicated posts later, but it also offers easy navigation to just those part of the solution you are currently thinking about (i.e. pattern to develop Rich Internet Apps - RIAs) that includes best practices and of course common pitfalls that you can encounter ...