A Plural God

So many of the Hebrew words we used to talk about God are all in the plural -- Elohim, Adonai (rather than adoni), Tzva'ot.

For a religion that's so staunchly monotheistic, this seems really peculiar to me. I really don't know what to make of this - except maybe to think that it's a relic from the polytheistic religions upon which Judaism was built. The thing about it that most puzzles me is that it sounds so Christian - a single God who we talk about in the plural?

How does Orthodox Judaism talk about this, if at all? Anyone know?