I think halcion is the strongest that's used in psychiatry. its mostly for sleep. not all doctors are so gung ho about it; back in the day, it was linked to some psychosis and suicide.

Other than that, there's xanax (and xanax xr) and klonopin, then ativan. I think there are some stronger bzd drugs used in pre-operative anaethesia, but I don't know anything about those.