I think you hardly can offend them, anything that is appropriate in America will be ok here (you are not going to give them underwear or anything anti-Russian, aren't you? )
If you know anything about their hobbies you could bring them something small, but useful and unavailable in Yekaterinburg stores. For any hobbyist it will be a pleasant surprise. If you don't..souvenirs or treats, maybe? Or something Christmas/New Year related, since you'll decorate New Year tree together. Maybe an angel on top or something, it's a bit exotic for Russia and will remind them about you.

Ok, I was not very useful here, but I'll keep thinking.