Insulating for A/C

[WisJim]

If you put in a roof fan for cooling purposes, you will also want to put in some kind of vents to allow air to flow into the attic space, so you have good circulation.

Light colored roof shingles make a big difference, too. Black roofs should be illegal on an energy saving basis.

[GasSavers_Ryland]

You can buy solar powered fan roof vents as well, they do cost a bit more but are self contaned so they will save you the cost of wiring, and save you on your electric bill.
The ground is pretty close to 55F all year round once you get below the frost line, the main reason for insulating the foundation of a house is to keep the cold from the frozen ground out, so in the summer nearly all that heat is coming from above, like was said, white, silver, grey, or any other light/reflective color will help keep your house cool in the summer, and in the winter those light colors will help keep the snow on your roof, and that snow will act, to a point, as insulation, keeping your roof 30F insted of the -10 that it might be outside.
while you are adding insulation to your atic, make sure that you don't block off any vents to the outside that might be in your eves, you can buy chanals that keep that space from filling with insulation so that you keep air in that unheated space moving, and most roof vents are labled with how many cubic feet of space they can vent so do your best to make sure you have enough.

[hawkgt647]

While you are in the attic, think about installing a radiant barrier. You can find rolls for sale on the web if you google it.