I was talking with some other photographers lately and the subject of lighting came up. The studio we were at had 6,000 watt seconds of power, including several power packs and some Alien Bees monolights. One of the other photographers asked me how I felt about the religious question of Packs vs. Monolights.
Really, when you get down to it, it's not clear cut. If you have four 400 w/s monolights, you have 1600 w/s of power total. You can get a power pack that has 1200 w/s of power and four heads. Depending on the design of the pack, you may have less total power from your four monolights (which is why many monolight makers talk about "effective" w/s of power) because often times it'll split the 1200 w/s of power evenly between however many heads are connected and use a controller on the flash heads to adjust further. However, if you have a pack and head system, you have the option of blasting 1200 w/s or more of power through a single head and a wider variety of head options that have built-in grids or lenses or such.
It used to be said that pack-and-head systems were better when you wanted to get a flash into a weird location or on a boom, but Alien Bees kinda blur that distinction given how tiny and lightweight they are.
Plus, there's the backup situation. If you have one pack and it breaks, you are out of luck. If you have a broken monolight, you are merely down one light.
Your natural inclination might be to get some of both, maybe one pack-and-head, plus a few monolights. However, you run into the problem that the speedrings that you use to attach between a light and a softbox or other light modifier aren't a standard fitting between brands. Softboxes are expensive and take a bunch of time to assemble and needing to swap speedrings is just going to get annoying. All of this discourages people from going between brands and also means that, if you need to rent lights to fill in a shortfall, you may have to rent the whole setup instead of just a few bits.
Now, truth be told, I own neither a pack-and-head nor a monolight setup. I'm a strobist. And I have a number of friends who have put off dabbling with off-camera lighting because they didn't like how much money it looked like it would cost.
There are definitely benefits to a "real" lighting setup. My sunpak 383 Supers have maybe 10-20 w/s of power, no modeling lights, imprecise adjustments compared to a good studio light, and don't recycle nearly as fast. But, on the other hand, I can drop two or three flashes in my camera bag and bring along a light stand and umbrella and shoot outdoors. If you want to do that with real strobes, you need either a generator or a battery setup, and both tend to get pricey and heavy.
Also, the minimum price for a flash-based setup is lower. Even with Alien Bees, you need to spend quite a lot of money to get a minimum setup. Your flash-based setup can start you out quite cheap, but still give you the sort of accessories that will come in handy if you move to a more elaborate setup, like umbrellas, reflectors, and stands.
I still maintain that your best "starter" setup looks something like this:
This is about the minimum required hardware to play with lighting. You can experiment with putting colored gels in front of the flash. You can tape paper to the flash with the gaffer's tape to spread out the light some. I usually point the flash upwards for this. You can put a reflector opposite the flash to "fill in" light from the other side. You can play with this outside or inside.
Play with the setup for a month or two, then get an umbrella. Play with *that* until you get sick of foamcore reflectors and want more lights. Some folks are quite content to stick with reflectors the whole time, others want tons of lights. It all boils down to what you feel comfortable with and what you end up doing with your lighting.
If you have a hotshoe on all of your cameras, you might consider getting the gadgetinfinity slaves off of eBay. Really, both options are a tad temperamental. The Wein Hotshoe slave is pretty industrially constructed, but you can run into situations where it won't get enough IR light to trigger off of. The gadgetinfinity slaves don't have that problem, but they are very cheaply constructed.
With the subject of triggering flashes, many Nikon flashes and even some bodies can be set manually to not preflash. Canon hardware is not so kind; only the 430EX, and 580EX out of the current lineup are able to trigger manually. I have a sunpak 144PC flash that won't preflash, but also doesn't have any manual control, so it works just fine. My old Canon A95 and my new Canon G7 both can be made to fire a single manually controlled flash.
You can buy a Wratten 87 polyester gel and cut it up, or you can use a piece of black slide film -- if you get a roll of 120 slide film, it'll be nice and wide.
This series is a time-lagged chronological journey through my off-camera lighting. I write about stuff that happens months after it really happens so I can get it organized and also to make sure that I don't writing a glowing review of something that turns out to be a piece of crap later on.
My goal with my off-camera setup is to be inexpensive (but not cheap) and portable and easy to deal with. It also has to work with my largely film-centric lifestyle.
I spent a bunch of time taking my 35mm camera and a flash in the camera bag to random events where I may want to photograph. Recently, I've instead been taking my G7 in one pocket and my 383 Super with an optical slave on the bottom in the other. If there's a white ceiling, I put the 383 Super on my G7 with no slave.. If there isn't, I leave the optical slave on and shoot with that.