If you're in the area, there's a lot more work to be done than medical and rescue work... which is rarely the sort of things they send volunteers to anyway. It doesn't matter what your skills are -- every possible specialty, including being a warm body, is needed.
I just went up to the Red Cross HQ and volunteered today, a couple hours after the attack. The first people they called forward (there were probably a thousand of us in a big high school auditorium) weren't people with paramedic skills or anything, but Human Resource professionals. Mobilizing thousands of volunteers is a logistical nightmare, and ANYONE who has these sort of skills is direly needed. Mental health professionals are also in very high demand, for obvious reasons.
But even if you aren't these things, there's mad work to be done. They said something to the effect of "If you're a computer geek, note that on your application. If you work at McDonalds, note it. If you speak Spanish, note it."
Rescuing people and giving them medical assistance isn't what you as a volunteer would do; everyone who can do that is already mobilized. But there's thousands of evacuees that have to be housed and fed, blood donors who need liquids and sugary snacks, and once the list of the dead starts to fill up, someone's gotta figure out whom the mental health professionals should contact with the bad news.
Nearly anything you can do, from data entry to flipping burgers, can be used to some good effect. Please help out; everyone (excluding felons I think) can be utilized. There is NOTHING, in my entire life, that has inspired me so much as the heroics and endless resolve of my fellow New Yorkers today.
(I do not speak for the Red Cross in any capacity; I am just an spontaneous volunteer who wandered in off the street this morning -- still in my slippers -- to see what I could do. I'm pretty much just repeating what they told me, as well as I can recall. So any inaccuracies herein are entirly the fault of my very tired mind.)
Perhaps we can do *snappy fun* with you everytime! -- Orz