I have decided to release my .NET Mapping engine. This is an alpha release, but it seems pretty stable. At the moment there are support for most types of vector data 
Take a look at the webpage, try it out, and contribute with ideas, bugs, comments, add-ons etc.: http://sharpmap.iter.dk

For desktop applications, there is a build-in user control that supports dynamic zoom and pan. I think it's pretty cool :-) For ASP.NET there are no user controls yet, but a HttpHandler to make life easier. Check out the FAQ.

You will need Visual Studio 2005 beta 2 to use it, as well as a PostGreSQL database with PostGIS extensions.
You can get a free Beta 2 Express Edition of Visual Studio 2005 here: http://lab.msdn.microsoft.com/express/vcsharp/default.aspx