Wanted to pass on my company Reykjavik Activity Center where you can book activity day tours like Painball, Icelandic SuperJeep safaris, arctic diving and snorkeling tours, and various other sightseeing tours.
Please take a look at our website http://www.rac.is for more information.
Also if you have any questions about day tours from Reykjavik don't hesitate to ask me here and I'll try to help you if I can.
PS. how do you like my site?