I find myself troubleshooting the same configuration issues with ASP.NET and IIS repeatedly. Usually I run into them infrequently enough that I forget what I did last time to fix them. I started a wiki at work to document the solutions but I decided to mirror them here for safe keeping. You can also access that section from the IIS and .NET Troubleshooting button at the top of the page.
If you have a solution or workaround for any other common issues feel free to add them in the comments.