ASAX - The Global.asax file, also known as the ASP.NET application file, is an optional file that contains code for responding to application-level events raised by ASP.NET or by HttpModules The ISAPI uses the System.Web.HttpForbiddenHandler to prevent direct requests to this file. This is the ASP.NET equivalent of the global.asa file
ASCX - Used for custom User Controls. When a page is executed with an ASCX reference, ASP.NET uses this extension to process the request. The ISAPI uses the System.Web.HttpForbiddenHandler to prevent direct requests to this file.
ASHX - Custom HttpHandler implemented as a file rather than a separate class.
ASMX - Files with these extensions contain the WebService processing directive and serves as the addressable entry point for XML Web services.
ASPX - Handles requests for ASP.NET requests. This is the ASP.NET equivalent to the .ASP extension.
AXD - Used to handle Trace requests (for debugging purposes).
REM - Used to handle .NET remoting.
SOAP - Also used in remoting and handling soap requests.
config, .cs, .licx, .vb, .csproj, .vbproj, .vsdisco, .webinfo, .resx, resources are all source code files. The ISAPI uses the System.Web.HttpForbiddenHandler to prevent direct requests to these files.