If you're looking for a welcoming group fitness environment and a REALLY good workout, Big Mike's Boot Camp is great. I went to his Saturday workout on 2/17 and was instantly impressed. Mike is extremely focused on teaching good form, and is efficient on time - making sure you get the most out of the hour or so you that spend with him.
I found such a welcoming, supportive, and encouraging group of people from all abilities, backgrounds, and lifestyles. It hurt so good. I felt really out of shape afterward, even though I go to the gym four days a week. I will definitely be attending Mike's Boot Camp every Saturday morning!