It's confusing on the Orthodox. I can't remember if Catholics can receive communion in an Orthodox Church (if absolutely necessary), but not the other way around, or the other way around.
When Anoreth and I attended a Greek Orthodox devotion last year, there was no communion, so we didn't have to get it straight!
I know that Pope Benedict (and I believe JP2) has celebrated masses with the Orthodox and I know that we may receive Communion in an Orthodox church if a Catholic mass is unavailable, but the meaning of that is vague. I'm not sure whether the Church allows the Orthodox to take communion at a Catholic mass, but I would think the policy would go both ways.
Sis married a Greek Orthodox in a Catholic wedding and they both received communion.