They usually roll out brand-new designs in the spring, and then new model-year cars after the summer factory shut-down in the following years. (ie, technically any E90s produced before September would be 2005 models, but BMW is marketing them as 2006 models because they are all-new. This is also why there are price and feature changes for September production cars.) In the future model years, the E90 will roll over model years in September, when the factories tools up after their summer break. Therefore, the 2007 E90s will almost assuredly start on the production line in September 2006.
As for deals, they will only get better the longer the car is on the market. You'll probably be able to get invoice+$1000 from the same salesman when you shop for a 2007. If you're lucky, the deal will get even sweeter.