I use these websites all the time!
Road.is: Road conditions in Iceland.
Vedur.is: Icelandic Meteorological Office, usefull for weather forecast, wind and even aurora forecast!
Gasvaktin.is: Petrol station locations and gas prices in Iceland.
Safetravel.is: Safetravel is the official source for safe travel in Iceland. Safetravel is run by ICE-SAR — The Icelandic Association for Search and Rescue.
Map.is: My most used website for researching, it has almost every road and trail and the quality of this satellite map is amazing, you can zoom in and still retain so much quality!
Go check out my guide for the best free things to do as well as itineraries and travel tips to make your trip unforgettable.