I had a really great conversation recently with Chris Tavares, the lead developer of the Unity Application Block for Microsoft. The chat was for my weekly article on InfoQ. Please check it out. 
Some information on Unity to get going:
- Introduction to Unity
- Downloading Unity
- Unity and Silverlight
- Using Unity and the ASP.NET MVC Preview 2
There are certainly a good number of Dependency Injection contains for .NET which have either been around for a long time or have sprung up recently. I am planning a post covering them in a bit of detail for those interested in learning about DI containers or understanding what is available.