I will be using a t2i. So a 580 & 430 combo is better than st-e2 & 2x 430? How so, can u elaborate more? I had always assume that 2 ocf is better than 1 ocf & 1 mounted. Thanks in advance for educating me.
The ST-E2 transmits its information to the remote flash units thru the small flash behind the red lens. It is a very low powered flash. The 580EX uses the main flash head to transmit the flash information. It is brighter and can be directed at the remote flash giving a longer range for the commands to be recognized. And it is not necessary to have the on-camera flash contribute to the image.
Since your original question had to do with ETTL only I didn't mention manual flash options. They are certainly less expensive and can give as good or better results, especially if you prize consistency. Manual flash is a bit more difficult to initially dial in for a given situation but I think the system gonzogolf recommended would work very well and save you some money. You could use that saved money to buy a good flash meter.
I still prefer ETTL for moving dynamic situations such as a child who wanders quickly. Manual, off camera units do not move as easily as ETTL units. Keep in mind that ETTL control with large modifiers (read softbox, large umbrellas, etc) can present additional problems since the ETTL slave has to be able to SEE the command flash.

