Vote for your favourite .NET DI (IoC) Framework

I've started to take a look at Dependency Injection Containers (IoC), mostly because we have started using them where I work and also just out of general interest and trying to get my mind around how they work. During my investigations I came around a load of .net IoC frameworks, a lot of them had their own pros and cons, and a lot of people were hard core supporters of certain frameworks. Currently where I work we have chosen to go with Castle. While on this site I am also looking at Ninject. Please bear in mind that I am new to the whole IoC principle and still have a lot to learn. So any input or knowledge will be taken on board!