Iceland-Reykjavik-was a wonderful place to visit, and might be one of my favorite trips so far!
An important thing we realized is that the cheapest/easiest way to get to the city from the airport is to take the FlyBus.
http://www.flybus.isThe company seems to have a monopoly in the area, and also use the name Reykjavik Exursions for their other trips. They will drop you off right at your hotel and/or the main bus station. They stop at the Blue Lagoon (absolute must-see!!) during the trip to/from the airport, but only certain trips during the day. You can save a lot of money that way, because otherwise you'll have to pay a separate bus trip with them to the Lagoon. However, we did it separate because that way we had more than 2 hours at the Blue Lagoon, which was really great! We stayed in there for 4 hours or so!
On all of our travels, we usually don't do any tour groups or anything and just do it alone. However, because of some of the driving warnings (small icy unmarked roads) we decided to just relax and have someone drive us around, the excursion company again, so we joined one of those tour bus groups for a day that took us around the Golden Circle-which includes Geysir, Gulfoss Falls, and all of the sites that Debinator mentioned in a previous post. It was well worth it! I know there are tours by boat to see Puffins, whale watching, etc. too.
The National Museum of Iceland was really nice. We also made it over to the zoo because I really wanted to see the Icelandic horses up close. It was a simple and small zoo, but a nice venture if you have some extra time.
Hot dogs are a major quick food over there, so that is a nice and cheap lunch to grab while your out. We were also surprised how many people were eating ice-cream
The weather in April was so crazy! It literally rained, snowed, hailed, and was so sunny I took my jacket off all in the same day! So dressing in layers is good advice!
I don't remember the sunlight ever being a problem at that time. We couldn't see the Northern Lights because of the time of year though.
We just stayed at a very simple and small B&B. If you have any other specific questions, feel free to PM me!