if you want to keep your 0-60 speed or race then a lightweight set of 16 or 17 are very practical.....you can put 18s on it aswell if your tuning the engine....
here is a few examples which i think are the most beatiful wheels ever made to sit under the arch of a e36......
http://www.turnermotorsport.com/imag...bs_rsgt_lg.jpg http://www.ab-tuning.ru/!rial/f/daytona-race.jpg http://www.tirerack.com/images/wheel..._3pc_ci3_l.jpg the above wheels are very expensive but make a mockery of my ****ty wheels... i regret not saving and getting them instead....
jap style wheels can work very well as well if the styling of the car suits it...
http://www.upgrademotoring.com/wheels/volk_racing.htm