Several new directories of importance have been created in ASP.NET 2.0.  The App_Code directory (formerly the code directory in Beta 1) is used to share code between pages without using a class library.  Classes files can be placed in this directory without being precompiled and they can be used anywhere in the application.  You can even have classes of different languages in subdirectories if you want. 
 
When you start working in Visual Studio 2005, you will notice that there is no longer a references folder.  Now, when you create a reference to another assembly, it simply places that DLL in the bin folder.

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