In all honesty, I think that this fight is MUCH closer than the Superman vs. Iceman fight we also have on these boards. Simply because Thor has so many different powers (thermoblast, and the absorbtion of energies).
Originally, I was thinking Iceman would win here the same way he would against Superman, but rethinking this, hmmm.
If we have BOTH characters at their full power, full potential? I'm going to say Iceman CAN win, but not the majority. Thor, 7/10
If we have Thor portrayed like the Hulk (SMASH! being his only thought), then I'll give it to Iceman 10/10 since there is nothing that can physically harm him.