Here is my set up for doing head shots and such. I just set it up in my living room, as I don't do enough studio work to justify a dedicated studio. I did an entire real estate office over the day, so it makes it worth while to set it up.
The bg light is the 36x48 softbox. The short stand (a 'plug' in grip speak) has a background light on it. With white backgrounds, you can change the colour by shifting the colour of the gel on the background light. There's a 52" fold up reflector as a fill source. It's out the frame, but I have a head mounted on a boom stand for a hair light. It's turned right down, and I just put a 'barn door' on the light, closed almost right up to keep the light from spilling onto the subject's face and shoulders. I have the subject sit on a stool, and I have a home depot work stand for the subject to put their elbows on. You should really have a proper posing table, but I couldn't find one for sale in Vancouver, and I found that for $25.00, and it works pretty well. I also use a digital photo target to set the white balance. If you're doing a home studio, it's really important to do an accurate relective white balance test, as your walls aren't a neutral colour, and you can get a crazy colour shift if you just set the camera to 'flash'.
If it's just one or two people in the shot, a relector is a good fill source. If it's more, you need to bring in a fourth light to fill. I couldn't tell you the size of the medium box, but it's about 24x36 inches, and you can peel the sides off so that it's like a huge stro-fen light. I really like beauty dishes, but they show so much detail that unless you've got someone with good skin and make-up, it's going to cause you problems.
Umbrellas are good light sources, but they spill light in every direction. If you're in a small set-up like this, you'll end up with light from your key light overpowering the background light and so on. I've been doing a lot of location work with my SB-800, and I really like using the umbrella with that set up.
David Buzzard's Technical Blog