I think that the 430EX is the best fit for most people. I find the 220 under powered and I hate the lack of bounce capability.
If you someday decide to use multiple flashes, you can add a 580EX and use the 430EX as a slave.
One drawback of the 430EX is that it allows less manual control than the 580EX. Well, the 420EX did, so I assume that the same applies to the 430EX. The main feature that you'll miss is the ability to set flash exposure compensation. If you have a 20D/30D/40D, you can do this in the camera, so it's not a big deal. If you have a Rebel (not sure about the XT or XTi), you cannot. That may not seem like a big deal, but being able to set flash exposure compensation is pretty important to getting good natural looking flash shots under a variety of conditions.
So I guess my advice is to get the 430EX if you camera supports flash exposure compensation (or if they've added that to the 430EX) and to upgrade to the 580EX if it does not.