I spent a summer in Norway as an exchange student after I graduated from high school and have been back once since. I am dying to go again. I LOVED it! Norway is fantastic for adventure- and nature-lovers but also has some great history and culture. The Oslo area is a great place to start, but if you're looking for more countryside, the area around Lillehammer (the Gubransdal valley) is absolutely stunning. Plus, you have Olympic Lillehammer right there. The Trondheim area is also fabulous, as are the islands in southern Norway. Lyngor is especially beautiful. I haven't been to Bergen, but that is supposed to be the "crown jewel" of Norway with the most beautiful fjords there. And the North is a great place to go in the summer -- that's on my list for the next trip.
I'm so jealous. You'll have a wonderful time!