I have not been to Iceland, but if I was to visit I would use Alex Cornell's Iceland Travel Guide. In the last several years, Iceland has been a hot destination to visit. Alex Cornell's guide Is very detailed especially when covering:

The Best Times to Go
Sample Itineraries
Sights to See
Where to Stay

Alex Cornell's Iceland Travel Guide

In conclusion, I wish most travel guides were as detailed. The creator of this guide is Alex Cornell, a Designer at Facebook and an amazing photographer. You can view Alex Cornell's Iceland Travel Guide through the following link.