Are there generic ones, or are there ones you can use entirely separate from the camera?
There's a crude option for any camera which allows you to manually set the shutter speed and aperture. What you want to do is set the shutter to 1 second or so (maybe half a second) and put your aperture fairly small (up around f/8 to f/11 would be good, depending on factors such as the strength of the flash and your distance to the subject).
Anyway, once the camera's set up, you just need a flash that allows you to manually fire it (often there's a "test" button or something on the flash unit). So you click the shutter, and while it's exposing, you pop the flash. Under normal lighting conditions this would result in a lot of blur, but in very dark situations the shutter is "exposed" but has nothing to capture, until you pop the flash. And since the flash is (ideally) a very fast event, it acts as if the shutter was exposed for only a very short period of time.
This has drawbacks of being unpredictable and unwieldy, but as the advantages of being very accessible and not requiring much in the way of equipment investment. It also gives you a wide DoF for nighttime shots, which helps offset the difficulties in getting focus right.
So that's it: One crude option that's cheap and requires a bit of practice.