Which Isolation Framework?

In the world of unit testing Isolation Frameworks are everywhere. Isolation Frameworks are very handy tools to help you create mock objects. According to Wikipedia:
“mock objects are simulated objects that mimic the behavior of real objects in controlled ways”

In the world of .NET there are a lot of tools out there to be used as Isolation Frameworks. There have been a lot of debate around the best isolation framework –Including this StackOverflow question.
If you have used any mocking framework, and felt like it’s a good tool to use, please vote on the poll on the left to this post or leave a comment about your experience with your preferred isolation framework.