Share 'What software do you use?'

So let me be the first bold soul to post to the forum. I've done some stop motion animation with my students this past year and have used a cool little free product called Stop Motion Animator. It's a little limited in what it can do, but, being free, you can't complain too much about that. What software do you guys use? What does it cost? Is it user friendly? Enquiring minds want to know.