I am not sure about those hotels but most NYC hotels honor the AAA discount (10-15% off). If you have an American Express platinum (or shoot... black!) card, they will usually give you a reduced rate too.
I've found that the best way is to usually call the hotels directly and ask them if they are running any promos or specials too. I stayed at the Benjamin during a major holiday weekend and managed to get a 2 room suite with free parking for less than $350 a night (most hotels of that calibur and size were going for about $700-1500 a night), just by calling and asking if they were running a promo special.
If you are willing to sacrifice location, there is a Ritz Carlton Battery Park that is located in (obviously) Battery Park, which is at the Southwestern tip of Manhattan island, closer to Ground Zero (and Century 21!). However, it is far far from 5th Ave, Madison Ave, Rockerfeller Center, etc.
Doing a spotcheck, the cheapest rack rate for Ritz Carlton Battery Park is $525/night v. Ritz Carlton Central Park is $895/night. Also, if anyone you know works for a large corporate that travels a lot (any of the big banks, Big 4 accounting firms, consulting firms, etc) you can ask them to try and book your stay using their corporate discount.
the only thing I can think of would be to book through orbitz and use the "EQUALITY100" promo code. It will save you $100. Compared to the overall cost of the stay, it's not much, but I guess it's $100 more that you have to spend while you are there!!