As far as I know, all top 7 except Columbia offer international loans without a cosigner. Tuck used to do so as well, but not anymore. Other schools that have such programs include Yale, Darden, Duke, Ross, Cornell, UCLA, UNC and Simon Rochester. Not all of them will cover the full cost of attendance though, so please visit the school websites for the details before deciding where to apply.
Thanks horrorshow- Simon's loan program has been a suprise to me; haven't seen that one to be honest. I guess they are the only school out of the (so called) top 20 to offer loans without US co-signers.