I just shop along Prince Street, West Broadway and Spring Street. Stores I like are Olive and Bette's, Big Drop and just the usual rest. I love the Market NYC it is one of my all time favorite places to shop for random pieces by new designers. It's on Mulberry Street and I think it's only open Saturdays (possibly Sundays but I would check). Good luck and have fun!
Also check out Broadway in Soho - that is where the big bloomingdales is. Really, as the other poster said, just walk between prince and spring, especially, on broadway, west broadway, and all the streets in between - you can start just after sullivan and work your way up and around. You can get off on the A, C or E at sullivan or the V, W (whatever the yellow trains are) at the corner of prince and broadway, or the 6 has a stop by spring and lafayette...it's all in the same area.