Poser 9 is the latest non Pro version. While Poser Pro 2012 the latest pro version is.

For service releases/updates you can check here: http://poser.smithmicro.com/updates.html

You can also order it from the same site. (http://poser.smithmicro.com/buy.html)

IIRC, I ordered my copy of PP2012 from there, as digital download version, as I'm on EU mainland.

From time to time there're special offers of the software, where you can get a very good bargain! You just have to keep an eye on things.