I'll second that. I started with a single 430EX II. Later, I got an MT-24EX to go on the MP-E 65mm I picked up, and started using the twin lite as a master to trigger the 430 to light the background.
A second 430EX II, Einstein 640 monolight, a PocketWizard MiniTT1, two FlexTT5s, a PowerMC2 and AC3, and a whole bunch of modifiers later, and I'm wondering what's next...