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I would recommend the 77mm version, a more standard diameter, and add a step up ring to adapt to other lenses (72mm->77mm in your case). I have used one on a 80-400mm for close-up photography and the results have been convincing.
++1. The 77mm will work on a wider variety of lenses. I expect part of the OP's problem is that he's looking for a non "standard" size of 72mm -- check ebay.
I don't do much in the way of closeups, so the 500D works well enough as a macro for me...