Now, come on...the "trust me, I'm a professional" line isn't the one to take in this instance. It's what added so much heat to this eight-hundred-plus-replies-and-growing thread.
I'm not saying there shouldn't be a canon, but I will say that the notion that Whitman (or any other author) is important shouldn't be taken at face value. Yes, Whitman was important to some writers, and less so to others. A nodding acquaintance with Whitman is probably required for cultural literacy at this late date (thank you, Academia), but the most relevant question I ask about Whitman is is Walt Whitman's poetry important to me.
The answer is no, not really. I once flabbergasted Virginia Tech's then-Playwright in Residence Jerry McGlown by telling him that my favorite poet was Robert Frost. A lefty like Jerry (R.I.P) couldn't imagine that that could be true.
Whitman is important, yes, but his work is most important within the particular version of the history of literature that the Academy has constructed for itself. That's fine, but if you don't mind, I'd prefer not to take the Academy's word for it. Give me some stacks full of primary sources and a thermos of coffee, and I'll form my own opinions, thanks.