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Can it just take any ETTL or other Canon flashes? If its true you could try a Sigma 500 DG Super, I have this flash and you sure get a lot for the money.
 
Given the direction that Nikon has taken with built-in wireless flash control in many of their DSLR bodies, I recommend that my customers go with the camera manufacturers flashes for future DSLR compatibility. It is possible that Canon may go this route too.

If you don't care about this, then there are many flashes that will work. Another name to look at is Promaster.
 
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