Colleen - judging by your avatar, you'd have no problem pulling off Sigourney Weaver. :D Though I doubt that he'd want to go dressed as an Alien so that might be pushing it a little.
You could try the James Bond theme for you guys ... he could go dressed in a tux (easy). You could put on a ball gown and be:
a) Xenia Onatopp (Famke Janssen)
or
b) Irina (Minnie Driver)
both from the movie Goldeneye. The majority of Bond girls are blonds so it does cut down your options ...
Masaki