Bored at a theatre rehearsal, I decided to test the limits of bounced flash with my 580EX II.
These guys are on a small platform, on a gym floor, with a white drop ceiling about 26 feet high. Flash was aimed straight up at it. 1/250 f/4 ISO 1600 (which means I could have done it with f/2.8 and ISO 800, or even f/1.4 and ISO 200 if I used a prime and didn't need much DOF).
Now maybe you don't like to shoot at ISO 1600. Get over it. By bouncing flash, you can use a bounce card for a bit of fill and get more pleasing illumination than direct flash, and you have the motion-stopping affect of flash (no worries about motion blur). You can also obliterate the puke-green colored sodium vapor lighting, and you have a bonus with the flash unit's AF assist light.
In case you think the ambient helped me out here, this shot was taken at the same camera settings but no flash.