Today I've discovered one of the coolest web parts I've never seen...the idea comes from the mind of Carlos Segura and essentialy it's a Sharepoint web part that permits you to write and test code directly into your Sharepoint site. The code is Visual Basic .NET based code (Visual Studio for Applications code).
More details about the usage are available on this post. This is really a cool idea, useful if you want to test little pieces of code that works directly with the Sharepoint engine.
You can download the web part from HERE.