I recommend Rhodes Service and Repair. I called them at 9:00 p.m. last Sunday and their Tech showed up at 10:30 p.m. then had our ac working again by 11:00 p.m. I feel they charged a fair price too, and the Tech was very nice - he showed us exactly what was wrong.
Also, according to their website, they do offer 24 hour emergency repair!
http://www.rhodesservice.com/