It varies between the E90 (sedan) and E92 (coupe). I can't speak for the coupe, but the sedan LCI (life cycle impulse) started with the 2009 model year. The main differences were revised front end, headlights, hood and taillights. It also was the first opportunity for the M-Sport on the sedan in the US. 2009 was also the first year for a HDD based Nav (versus DVD). I believe there were some minor tweaks to the interior for 2010 as well, but I think I hit on the major items.
2010 E90 335i Black Sapphire
Best Stock 1/4 time = 14.1 @ 99.4 at Bandimere Speedway (DA = 7,400ft ASL; 13.5 @ 103 corrected)