Wikipedia has a pretty thorough description of Orthodoxy:
http://en.wikipedia.org/wiki/Eastern_Orthodoxy.
The main differences from Catholicism: Orthodox churches use icons, especially Russian churches. Varying degrees of importance placed on the individual sacraments and the processes in which they are administered. Slight differences in the Creed and Lord's Prayer. Theological opinions of the importance of faith and good works. And the structure of the church itself--each Archdiocese is seen as independent and of equal authority, altough the Archbishop of Constantinople generally is seen as having the most wisdom or insight.
There are probably more differences, and I have probaby given some slightly inaccurate information, but this was just off the top of my head.
And don't worry about adding Orthodoxy into the poll, since I don't think you can change polls, and it's not quite as big of a deal as I may have made it seem.
As for the topic of predestination, I'm fairly sure that Orthodox theologians do not think it's a valid theory, since great importance is placed on good works and faith in determining an individual's salvation.
Oh, before I go, I'll give an interesting tidbit! Luther, as he was pondering the problem of the authority of the Roman Catholic Pope, learned that a whole different set of churches existed to the East; he had no prior knowledge whatsoever of Orthodoxy. He then used this in his theology, saying that Catholism cannot be the "true" church, since the true church should contain
all Christians everywhere. This gave Luther that last little push he needed to combat papal authority, although I don't think he ever actually commented on the validity of Orthodoxy, which I find odd and incomplete, yet still somewhat flattering.