So you have a road trip around Iceland coming up but you're not quite sure what the road conditions and the weather will be like (the weather part will also determine whether you need to pack your winter coat or not). The following websites are your friends and they will show you just what you need to know. We found them very useful during our visit.
For road conditions, make sure you bookmark Vegagerdin (Icelandic Department of Transportation) website. This clickable road condition map is essential. Don't hit the road before consulting it first. If that's not enough and you need to know what road conditions are like in (almost) real-time, there are road web cams, ready for your perusal.
For weather forecast, Vedur (Icelandic Met Office) website is the one to bookmark. It has a clickable map of Iceland with a 6-day forecast. It even has a map with weather for areas around popular tourist attractions. Very handy! Tip: For something different, scroll down the page and play the sound file of an Icelandic person reading the weather forecast in English. Icelandic accent is adorable. :-)
Another website you might want to bookmark is Live from Iceland. It has live streaming webcams from various attractions in South Iceland, including Reykjavik. My husband loves watching the one of Geysir (I'd recommend waiting a bit until you see the one geyser called Strokkur erupt -- it won't be long). I love the Jökulsárlón one. Anyway, you can see what the weather's like at those places in real time and even can arrange to have someone at home watch you have a blast through the webcams!
I hope someone will find this post useful. Have fun in Iceland!