Honestly all flash heads would work.
your real problem would be
1. the connections – if they are hot shoes or plugs etc.
2. you cant use the 3D matrix metering
3. you can't use +/- flash compensation
You can use A and Manual
Right after the shot you can decide on how the image looks and adjust from there. [...]

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10.1MP, 3888×2592, CompactFlash Slot
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Technorati Tags: camera, canon, digital, EOS, rebel, slr, XTi

I'm looking to buy a speedlite for my Canon Rebel XTi camera. Can anyone give me any pointers please.
Define "best."
The high end Speedlite is the 580EX. Not only does it have maximum power, but it will also wirelessly control other Speedlites.
There's a 580EX II on its way to market that replaces the [...]