It depends on where you live, of course, but where I live there are lots of things decorated pretty specifically for Hannukah - all silver and blue, at least, and some having stars of David or driedels or something. Too late for this year, since you've already bought something, but if you wanted to, you could probably find something specific.
A few times I've gotten my Jewish friends some of those chocolate (kosher) coins - gelt is it? or something like that? They are traditional for Hannukah, and my friends seemed to like it.
I have one Jewish friend who prefers not to make too much of Hannukah personally, because she feels it's morphed by it's relation to Christmas, but that just affects how *she* treats it - she's never offended, and in fact she's touched, when people try to include her like you're trying to do with your coworker.