The 430EXs are also great flashes, and more than enough to do any fill work you may want, and a great way to get your feet wet with flash. A lot of folks buy the 430EX first to dip their toe in the pond. Given the current price on the 430EX, it's a relatively painless way to get a great addition to your system.
But I do want to also throw out there the possibility of getting a used 580EX. It's missing features compared to the 580EXII: no camera menu control, no weather-sealing, no fastlock shoe, no auto-thyristor, or PC port, and slower/louder to recycle. But on the used market, they're going for ~$300, so if you can get a good price, it's not that much more than a 430EXII. And you get all the other stuff on the list, including the higher power and 360° swivel. If you're willing to go back another generation to the 550EX, it's about $200-225. (No 360° swivel, a little less power, and commanding is only groups/ratios).
Do not, however, consider a 420EX--there's no manual control of power, so it's not so good for the Strobist thang.
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