That is really a difficult question. It depends on what you have, where you are shooting and what you are going for. I know that is annoyingly vague. I do my indoor portraits with strobes and usually only use 2. When I do outdoor portraits, I just time it where the sun is not overhead and occasionally use a reflector.

You could spend thousands, or you could use the flash on your camera. Your on board flash will give a more "flashed" look.