I would absolutely recommend going a trip up north, atleast just to experience the midnight sun. How about taking a day in Tromsø before continuing on to Iceland?

Geirangerfjorden is a definate MUST-SEE. I take it you're renting a car? Personally, I'd take a car, and drive from Oslo to Bergen, and then continue up north along the coastline, crossing the atlantic road and continuing all the way up to Tromsø, before flying to Iceland. I rode a motorcycle from Oslo (via Volda, which is a bit farther north than Bergen, but still on the west), back again to Geirangerfjorden, out to Molde and along the coast up to Trondheim. From there, we drove along the E6, but if you're in a car I would recommend the more scenic E17 - the coastal route, also called "The golden detour".

It will take you a day or three to complete the drive, but it's absolutely worth it.