Invest in a graduate schools book. Plenty of schools take people for certain programs with a 2.7+ and probably one or two take people with a 2.5 +. Below this, I'd think about retaking some courses you didn't do very well in. Where there is a will, there is a way. Historically, I have found it helpful to contact someone in a program you are interested in, tell them your situation, and let them tell you what you have to do to have a good shot at their program.