There are a lot of places to look for Microsoft documentation currently online. Depending on the area that you are focused in, you may have to visit any of a number of sites to get the information that you require.
One of the best places to start is with the ASP.NET Wiki. This site was designed to collect all the different links from around the Microsoft web properties dealing with ASP.NET and bring them together in one place.
If you can't find it there, here are some other places to look that will have a lot of information on different topics:
- ASP.NET Learn page
- ASP.NET Get Started page
- IIS Learn page
- IIS Get Started page
- Silverlight Learn page
- Silverlight Get Started page
- MSDN ASP.NET page
- MSDN ASP.NET Learn page
Of course, you can also look at the various blogs that are out there and get a lot of information from them. See my previous post here for links to some of them.