The first thing you should really do is ask yourself one question. What do I want to get out of the car. If you want performance and handling, you have to see all of what you have to do to get the car in the shape that you want. A sway bar alone won't give you alot, if anything unless it's matched with sport springs, shocks/struts that will give the car overall better handling.
Eibach and H&R make very good products. Also Ireland Engineering does alot of suspension components for the E30 too. If you need any help or any questions you can shoot me a pm anytime. Best of luck. I wish I still had my E30 still.