TGI....Monday?

A friend of mine (although not a good enough friend that she ever reads my blog, arhg!) is coming into town tonight and I've taken the day off work tomorrow. The request for her big night out in the city is dancing. Anyone know somewhere good to go out Monday night? Must be cheap or free and Brooklyn is a plus. Providers of good tips will be rewarded with credit online as well as my ongoing love and affection.