First and foremost thanks to all that post with such great information! Even though I may not post a bunch, I sure do read a lot! so thank you!
I was there with my daughter (who stayed an additional 7 days for school related activities) for 4 days/3 nights.
We flew overnight and arrived at 7am. We had tickets for the Flybus--went very well. We arrived at our hotel Centerhotel Arnarhvoll - and did the early check in for 40 Euros. For me this was well worth it. It included breakfast for 2 and a chance to lay down for a couple hours before the sun came up! Plus I was able to talk us into a room with an awesome view!
The staff at the hotel was awesome. They were very helpful in us getting around, find places to eat, rent a car and finding my way to places I could not find on gps. The breakfast is the same every morning but enough variety for a few nights stay. Also the breakfast room is a bar at night. Nothing fancy and low key but was awesome to go upstairs and chill with a drink reliving the day and planning the next day!
After getting our energy back from flying we planned to just walk around town. the sun was mostly out, but very windy and temps around 1 degree Celsius. We had a great time walking around and seeing the town. Going up the Hallgrímskirkja church is a must do! beautiful views.
We grabbed a hot dog a the famous hot dog stand (get crunchy onions if you like onions) for lunch. Was a line and a good hot dog. We later went to dinner at Icelandic Fish and Chips. Very casual place and good food if you like fried fish. the batter is supposed to be healthier, I don know about that but it certainly was lighter batter and very good.
At night we went with Superjeep.IS for Northern Lights tour. The trip up the mountain to see the town at night was thrilling and scary! Then the chase was on. We luckily got to see the lights near the end of the night (almost midnight). They were not very strong, and I would have never been able to pick that on my own. Overall a good experience and would go with them again.
Day 2 rented a car since the weather conditions looked like they were going to hold. Rented from procars just up the street form the hotel. Also rented a gps that was pre-programmed with all the big sights on the most popular tours. I highly recommend this, made it so easy to get to the places we wanted as it came with a book explaining what was at each sight and a picture. With only 5 hours of day light this helped maximized our time for what we were interested in! Golden Circle drive may be one of the most scenic drives I have ever taken. Very easy to drive--assuming no bad weather! Dinner that night we went to a place in town and I cant think of the name. A shame because the salmon was very good. sorry.
Day 3 we kept the car and headed on the south cost tour with the trusty gps! again flawless! We went down to Vik and just loved it. Again beautiful, a little more driving and longer stretches of driving then Golden Circle, but highly recommended. There were stretches we drove without seeing another car for 10-15 minutes. Loved this area though. The waterfalls are dramatic!
Again I cant remember dinner but I know we enjoyed it! :)
Next morning we got up and I had to take my daughter to the university to meet with her group for the week. That went well and went to return the car and they offered a free ride back to the airport. However, they had no one available to take me. So they just let me keep the car and return to their location by the airport and that office drove me back to the airport, no additional charge. That worked for me!
All in all LOVED Iceland. And I cant wait to get back.
My biggest piece of advice is make sure you have clothes that will help block the wind! We did and it made a huge difference in how long we were able to stay outside.
Here are some pictures of our trip if interested.