Light, as they say, "is light." The most important characteristic of monolights, or any kind of lighting system, is the quality and the quantity of the light they produce. Other stuff like recycling time, power control, build quality, and the ability to accept accessories are important, too, but none more so than price. Adorama (www.adorama.com) offers two series of modestly priced monolights, including the Flashpoint II and compact, almost tiny, DigiPoppers, both of which fit within the budget of almost any photographer who needs studio lights.
Don't let the cutesey-poo name fool you; these are nicely made little monolights that will make a great starter set for the new photographer or any photographer on a budget. Yeah, they're mostly plastic, but the reflector is metal and can handle any umbrella with a diameter of 8-10mm. Each DigiPopper's reflector was a good companion to the 45" F.J. Westcott (www.fjwestcott.com) umbrellas I use, but a 32" might be a better fit for single portraits or headshots.
Despite their "Barbie's Own Monolight" appearance, the DigiPopper 200 and 300 models I tested were rugged enough for location photography--if you pack 'em in a case while traveling. Not so rugged are the Popper's modeling lights, which can be fragile. One of them was DOA when I opened the box it was shipped in and while Adorama quickly replaced it, I broke another while setting up later. The cost of the modeling lights is only $8.95 so you might want to order a spare--or two.
Adorama offers lots of different accessories for the Poppers, including barn doors and snoots. If you want to create a lighting kit that'll fit into a tiny case, you might consider using Westcott's 42" collapsible umbrellas that take less than half the space of conventional bumbershoots. A wonderful complement to these lights would be a pair of Manfrotto's (www.bogenimaging.us) Nano (light) Stands that would make a very small location lighting package indeed, and I'm working on it.
Flashpoint II Series
The Flashpoint II monolights are compact and lightweight and are clearly designed for more professional use. They have proportional halogen modeling lamps, variable flash power settings, audible flash-ready signals, and built-in slaves.
A rear-mounted handgrip makes for quick positioning and it's easy to schlep the Flashpoint II monolights around. A knob lets you set power output and the dial is continuously variable so you can set it anywhere to establish a specific f/stop that you might want to use for a particular shot. Like the DigiPoppers, Flashpoint II has a built-in switchable slave, but with more rugged controls.