When I was creating my new blog site (this site your looking at), I chose to write it in C#. I had a problem with the App_Code folder because I had some code in VB.NET code and some C# code I needed to put in there. I didn't want to rewrite my VB.NET code in the App_Code folder just so I could write the rest of the code for the site in C#.
Luckily, the ASP.NET Team had already thought about just this kind of circumstance. They implemented a way to partition the App_Code folder into sub-folders, one for each set of code files written in the same programming language. Awesome, I didn't have to spend a couple hours converting code from VB.NET to C#!
The below works with ASP.NET 2.0 and later.
Even if you don't use multiple different programming languages for your code files in the App_Code folder, you could use this feature to organize your sets of related code files into sub-folders.
Step 1: Add the following lines to the web.config
Step 2: Create a sub-folder in the App_Code folder for each language you want to support.
Step 3: Place your VB.NET code in the VB_Code folder and place C# code in the CS_Code folder.