The kiosk can create a duplicate key for $19.99 and stores the digital copy for free for future keys, available for an additional $3.49 per copy. Fingerprint identification and email notification add a layer of security, much safer than the "key under the doormat" routine.
More information about KeyMe at their website.
Live outside of Manhattan and need a new key? Plan in advance of misplacing a key and check out Shloosl, a key duplication service which converts digital photos taken with your phone into brand new keys sent back by mail.