I've known about Mockito for a little while, but I've only just now officially tried it today, and Sczepan Faber (and friends) are now my bartenders, and when it comes to mocking, a nice cold mockito is my new drink of choice.
Wow. Seriously, wow.
The syntax is exceptionally sweet, and additionally quite clever. A coworker and I dived into how it figures out what method to stub today and that alone was enjoyable.
Mockito will definitely be a valuable tool to have in the testing toolbox.