One of my favorite ASP.NET features is forms authentication, supported by the powerful membership system in ASP.NET 2.0. Back when I built Web applications for a living, I remember agonizing over the building the authentication support for my applications. What developer wants to spend time building authentication infrastructure, tying it intimately to a custom-built membership store, and subjecting your application and server to SQL injection and cross-site scripting attacks, when you'd rather just focus on the app itself? I won't spin any longer on ASP.NET forms auth and membership virtues, but if you are new to these features, check out this content on Scott's blog.
With the introduction of Integrated Pipeline in IIS7, ASP.NET Forms Auth and Membership just got a lot more powerful. Now it can be used with all types of content including classic ASP applications, Cold Fusion, PHP, Static files, or any other type of request. In this video, which I posted a few weeks back in preparation for MIX, you can see how to get forms auth against the SQL membership provider working for a PHP application.