I don't have a NYC Metro Card, but I hope to in the future. When I do, dadhoc's Slim Wallet with Metro Card Sliding Compartment on Thingiverse is where I want to keep it!
Thingiverse link: http://www.thingiverse.com/make:66460
Settings: Printed perfectly on a Replicator 2 with MakerWare on .3mm/low, no raft and no supports. The middle divider is just one path thick, and the overhang clip printed with no problems. Excellent design, dadhoc!
Stuff to change: Later I'd like to modify this design to make a Metro Card and small cash compartment that I can clip to the inside of my messenger bag.