We just got a new generation iMac13,2 , i.e. the 'Late 2012' model.
We choose the following configuration:
27inch, Intel Core i5, 3.2GHz
8GB RAM
1TB Fusion Drive
NVIDIA GeForce GTX 680MX 2GB GDDR5
AppleCare Protection Plan
This so far is ample of power for a regular AC16 workstation, but ultimately depends on what other software you need to run... e.g. most rendering or post processing / video editing software might benefit from additional RAM and faster harddrives.