What is the IATA code for the A320neo family?
The IATA three letter code for the Neo will likely be the same as for the regular model. 
Unfortunately the IATA code list is copyrighted, and I can't find a public document that confirms it. 

The more commonly used ICAO type designator, a four letter code can be found in  ICAO doc 8643. It contains a list of all common aircraft and their codes. 

The ICAO type designator for the neo will be the same as for the regular versions. So A319, A320 and A321. Only if the performance of the Neo aircraft significantly differs from the originals, then a dedicated designator will be created.