Seminar Systems; Response Mail Express
It's joined to http://www.seminarsuccess.com/
It kind of goes the high cost/quality approach. On the lower cost side there is "Seminar Crowds", "Seminar Direct" is another outsource company.
Experiences? Comparisons? Recommendations? etc.
I have used them, they are solid. They get the people there that is for sure, its just up to you after that point. I liked there service and will use them again.