Chuck Hayes is a name that certainly stands out.
At 6'6, he's still one of the post defenders in the game. While he'd still be undersized, I can't imagine what an extra 2 inches would do for him.
Luis Scola is another guy that I didn't see get mentioned, though I guess he's just a lesser example of Zach Randolph.
Wonder how Dwyane Wade's career would turn out. Would an extra two inches at least prolong his career? at 6'6 he's probably not taking the same kind of hits he has throughout his career. Though he'd probably not be quite as quick.