Low GI = 55 or less
Medium GI = 56 - 69
High GI = 70 or more
GI intrigues me to say the least. It is not really a quantifiable approach, glycemic load as mentioned is much better. As I posted before, gi in and of itself is dubious at best. Witness that M&M's peanut are lower on the gi scale than canned pinto beans. Does this make sense for your diet?
I would be sure to incorporate the Insulin Index as well for foods. Some of those tricky foods can show up low to moderate on the GI/GL and still high on the II(see above paragraph)...when it comes down to it, blood insulin levels are more important to moderate than glucose levels.