Is there a web service that does reverse FirstBits lookup? Input: any old Bitcoin address e.g. 

1BCNEPySL4gzzjg8NNyNsQYJWYmZwpgaPF

Output: the FirstBits, in this case 1BCN1u
Blockchain.info has APIs to generate and resolve firstbits.

Get firstbits,

http://blockchain.info/q/getfirstbits/1BCNEPySL4gzzjg8NNyNsQYJWYmZwpgaPF

Get address,

http://blockchain.info/q/resolvefirstbits/1paypal

http://blockchain.info/q/resolvefirstbits/1ebay

http://blockchain.info/q/resolvefirstbits/1google