Iceland's so small there really isn't any monster.com type job listing site. Jobs that are advertised are generally in the newspaper, so you can find some on these two newspaper sites:
http://www.mbl.is/atvinna/http://visir.is/section/RAD#subkat=2
as you see, not many jobs listed, and at the moment, none are graphic designers.
If I were looking for a job like that in Iceland, I'd probably just do a net search in English and then send emails to offices I found that way. If they've got an English website, they're presumably not against hiring people who speak English. If you have a good online portfolio, you never know what might happen.
it'd also be good to plan a trip to Iceland so you can write to them and say "here's my great work, I'd love to talk about career opportunities at your place when I visit Reykjavik on these dates"
Yes, you are absolutely right about how small is Iceland to have a monster.com website. I have made an internet research and I have found some nice graphic design offices thanks to LinkedIn; I'm not looking for the well-know international advertising company; I couldn't work in a working environment like this anyway and, to tell the truth, I would be so naive to believe I could find one!
I had also found a couple of newspapers; one is in English, and they post some jobs from time to time but I never saw any graphic designer jobs till now. I didn't know about those you posted, so thank for sharing these two links. Even they are in Icelandic, google translator might help me a little bit to have an idea.
So, thank you again for all you kind advices.
Have a lovely weekend,
Lena