For those of you ASP.NET developers who haven't tried (or, somehow, haven't heard of) Elmah as a solution for error logging: version 2, which has been around since last year, is still great.
Implemented as an HTTP Handler, it provides a clean way to log and review any unhandled errors thrown by your ASP.NET application. I prefer the SQL Server storage method (a single table and some stored procedures), but XML is an option. Run the script in your database, add some entries to the web.config file, drop the DLL in your bin directory, and you're good to go. The handler provides access to an error review page, which shows the detailed error information, as if you had been running the application and the error was thrown in front of you (i.e. it mimics the standard ASP.NET detailed error page).
It even provides an RSS feed to the error log. Highly useful! Again, if you haven't tried it, I highly recommend it. It's easy and quick to setup, and may save you a ton of headache in the future. You can find the binaries and the source code here: http://code.google.com/p/elmah/