If you are not a dress person there is still a lot of choice out there. The jumpsuit is becoming increasingly popular and fits in with the whole '70s revival that is gathering pace. The most flattering are tailored with either a wide leg or peg leg, as opposed to the harem style with elsasticated cuff.
Don't rule out trousers as party wear!
Drew Barrymore paired Camilla and Marc high waisted trousers with a sequinned top by Richard Chai for an appearance on the Letterman show to promote Going the Distance - a chic look which would easily translate to the office party.