Turbo

All current diesel models have turbochargers. The e92 335i and the E82 135i have 3 litre twin-turbocharged petrol engines. :)

Also the upcoming M/// series models are about to acquire Turbo. The new M5 will be replaced with a V8 Turbo or Twin Turbo engine. !!

likewise with the F01/F02 7 series :)

I dont think the M3 is gonna get a turbo... that would be awesome, but i just dont see BMW doing it. as for the M5, i'd say it would be a twin turbo V8 for sure.

Currently (MY 2012), the BMW 328i, 528i, and Z4 xD28i has the newest 2.0 Litre TwinTrubo engine that BMW just recently manufactured, making 240hq/260tq. The BMW 135i, 335i/is, 535i, 640i, 740i/Li, X3 xD35i, X5 xD35i, X6 xD35i, and the Z4 xD35i/is have BMW's famous 3.0 Litre Inline-6 Twin Turbo engines that produces 300hp/300tq (the 640, 740 has a tweaked twin turbo engine that makes 315hp/332tq, and 315hp/330tq, respectively; whereas the 335is/Z4xD35is makes 320hp/332tq, and 335hp/332tq respectively). All the V8 counterparts also acquired TwinPower Turbo (as BMW descrbies it), which you can find in the 550i, 650i, 750i/iL/ActiveHybrid, X5 xD50i, and X6 xD50i, which makes a respectable 400hq/450tq. Of course, you have the X5M, X6M, and the upcoming M5, which has the tweaked version of the aforementioned TwinTrubo V8, which makes 555hp/500tq. Last but not least you have the 760Li, sporting a TwinTrubo V12, making a snarling 535hq/550tq, which is the largest Turbo Engine BMW has ever made. Almost all of the BMWs have turbo engines now.. you can only find very few cars now still featuring the good ol' naturally aspired Inine-6 engine (the 128i and 328i coupes). Why did BMW do this to all of its line of cars? Horsepower wars w/ other luxury manufacturers? Definitely. Fuel efficiency? Perhaps. Will it be as smooth as the naturally aspired? Yet to evaluate. Hope this clarifies some of your confusion.