I went to Iceland for a week in 2008 and loved it. I thought the Blue Lagoon was overrated, but I'm not big into spa stuff. It was pretty though.
Definitely go check out the waterfalls.
I did a number of daytrips via
Reykjavik Excursions. I don't recall the specific trips we did, though I'm pretty sure the Golden Circle was one of them. The absolute best thing I did there was see the Aurora Borealis, but with the amount of daylight right now, I'm not sure you'll be able to do that. I went in late September/early October.
I had a fantastic dinner at
Tapas Barinn. Definitely recommend that. Everything in the city was pretty expensive so I could only do one nice dinner, so this was a great way to try a number of dishes in the tapas style. I had puffin and whale, among other things. It looks like they have a specific
Icelandic Gourmet menu choice. Then we also did very basic (and inexpensive!) lunch one day at a hot dog place called Bæjarins Beztu Pylsur. Pretty good!
From paging back through my digital photo album, I'll recap some of my favorite places outside the city. I also had fun wandering around Reykjavik itself.
Gullfoss waterfall:
Strokkur geyser:
Thingvellir (Þingvellir) National Park:
some history at Skógasafn (c. 1850):
Skogafoss waterfall:
Black sand beach and white snow, in Vík í Myrdal:
Seljalandsfoss waterfall:
You could go behind Seljalandsfoss too:
We also went out to the glacier tongue Sólheimajökull from the Mýrdalsjökull glacier, but the pictures I have online from that aren't great though it was pretty awesome to climb on a glacier.