Mississippi gives an interesting option for bad grades. You can basically start and any year, and they will only incorporate from that point on. In other words, if your freshman and sophomore years are horrid, and you started over, they will count from your junior onward.
There is a caveat however - ALL of your required classes must be retaken from that point on. If you have an English or math class from freshman year, you would need to retake it.
I am sure there are some other nuances to it, but thats the gist as it was explained to me.
They also take the higher of your 2 grades for your science and math average (but average all grades when calc. your GPA)