OpenID authentication in ASP.NET?
See Scott Hanselman's post on using DotNetOpenID in ASP.NET. Andrew Arnott's blog is full of samples on using DotNetOpenID with ASP.NET, including ASP.NET MVC.
I recently hooked up DotNetOpenID for the Subtext 2.0 release. It went really smoothly - the code samples included with the DotNetOpenID download are pretty helpful. The one thing I'd recommend is that you just use the library and avoid the ASP.NET control. It uses table based layout (hardcoded) and is pretty difficult to restyle.
Are there any good tutorials on how to integrate OpenId with an ASP.NET site?
Andrew Arnott's post titled "How to add OpenID to your ASP.NET web site (in C# or VB.NET)"