I've always thought that omniscience cancels out free will, but I also think omnipotence cancels out free will too. If God is all powerful, the law of unintended consequences (that every action affects something else whether it is intentional or not) would affect all of his decisions. The only way to circumvent this would be that god would have to be omniscient, so that all of the consequences would be known by him. In my opinon, if there is a god in the judeo-christian/islamic sense, we would not have free will. I'll admit that my own ideas about theism are very vague, and seeing as I haven't had a millenium of thinkers working out the theological kinks of my own musings, it isn't very developed.