There are different resources depending on your interests. ASP.Net is the sibling of PHP, ColdFusion, JSP and other server-side languages.
ASP.Net is developed to be used as a Rapid application development platform, in that it together with Visual Studio often is able to get you up and running very quickly.
ASP.Net gives you:
Master pages (like templates in php)
User authentication (verifying visitors) and authorization (verifying that they are authorized to request resources).
A choice - either develop you app quickly with drag-and-drop from the toolbox, or go learn the more advanced stuff (see below) that lets you port applications to linux and integrate them with enterprise systems.
the possibility to use numerous frameworks that extends the already very large .Net framework.
support to load external datasources asynchronously, as opposed to e.g. PHP which doesn't have that support.
a page model where you don't always have to write $_GET['lalala'], but rather controlname.Text.
ASP.Net is a framework that lets you learn as you go - you can get your first hello-world application up and running in a few minutes, and most common stuff can be accomplished using the built-in features, but you can excel as far as you want, learning more and more of the programming language of your choice (most often c#).
This opens up a world of design patterns and application architecture much entangled with the world of Java which has had and has its widest adoption in an academic context.
http://castleproject.org/ - useful resources for advanced applications. However, if you're a beginner and you find the ASP.Net syntax (1) hard to learn, go with MonoRail instead. This project combines the web syntax of Ruby-on-Rails with the great (as in big) .Net Framework as the back-end and easily integrates with e.g. NHibernate and unit testing because it demands a Model-Controller-View separation of concerns.