We can't give you a winning number. In terms of low gpa, you should not think of it in terms of an average. Fewer people get accepted in the low GPA bracket, and those people usually stand out elsewhere (GRE scores, extracurriculars, exceptional circumstances, etc.). Check out the "Successful Applicants" threads to get an idea of what people's stats look like.
That said, the average all-around GPA for accepted students is probably close to a 3.6. Some schools have a minimum requirement of a 3.0. There others that may have a cutoff below that, I don't know which ones off the top of my head.