Giro HV are the wide versions of Giro Shoes. Check out the Privateer.
Shimano do wide fitting versions of their shoes/boots. I own the wide version of the RC-7 road shoes. They aren't that wide though.
Researching I came across a forum thread recommending the Shimano mt41 and the Shimano M089 in wide fit.
Sidi do an ultra-wide fit. One forum post recommended the SIDI Mega fit claiming they were the best shoes they had owned. More on Chainreactioncycles.
Some people said that Specialized were wider than most but again not the widest.
All Bontrager cycling shoes tended to come up wider according to forum posts I read.
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