I specifically want to rent the Canon 5D body this weekend because I will be shooting the antiwar protest. But I am not from NY so I have no idea where to begin looking. However, I imagine if any city will have a place that rents 5Ds, it would be NYC.
I had already looked on BH's Website, typed in "rentals" in the search section and received a page that said, "Sorry, we currently do not offer any rentals."
You might try Adorama. If they don't do it "Lens and Repro" cerainly do. Expect to pay $200/day and don't expect to pick one up on a Saturday!
Adorama: http://www.adoramarentals.com/ I rented a 70-200 f/2.8LIS there in February. Very good service and you can reserve online. I reserved the non-IS version, but when I went to pick up the lens all they had was the IS version, which they gave me for the lesser price of the non-IS lens.