When I shot the Tribe party recently, I was not the only photographer using a Gary Fong Lightsphere:
In general, where there’s no obvious bounce surfaces, the Fong Lightsphere is what I will turn to. No panacea, but a good tool to have in your bag. The Lightsphere throws light in all directions, and there is a good chance that something will bounce back light.
And of course open your lens all the way f/1.4 is better than f/2.8 when the light is low. And 2.8 is better than 4. And 4 is better than 5.6… you get the picture.