The E28 like most BMW's, comes with front brakes that are more than adequate for street driving. Just think of what the Big Three put on the front of their cars in the 80's in comparison! Some people can get by with good pads (racing pads, not Metal Masters!) on the track. In fact, most problems with the front brakes (warped rotors or the dreaded shimmy) are really due to the upper control arm bushings, not inadequate brake size. Fix your bushing problems first, then worry about upgrading the brakes.
When you really need more front brake, the easiest and cheapest upgrade is to use the front rotors, calipers, and brackets from an E32 7 series.
The E32 brakes fit under most 15" wheels. The thought of running 17" wheels year round in NJ scares me, as I've bent enough 16" alloys to build an Audi. The calipers are widely available used, so don't pay more than $130 a pair with brackets. I got mine from Zionsville Autosport. You can use your original brake line. Because this caliper uses the same pad as an E36 M3 (I think), there are a wide variety of pad compounds available. For the street, I run factory pads (Pagids). I have had good luck at the track with carbon kevlar pads. After warping an Ate Super-whatever rotor with the groove, I exclusively run Balo brand rotors from Steve D. at The Ultimate Garage. These are the finest OE type rotors I have seen. The non-directional ground finish on the rotor surface is fantastic!
A few places (Korman, Bekkers, and others) sell a Brembo caliper kit that fits under 16" rims for about $1600. This kit is comprised of a pair of Brembo calipers, E32 rotors, caliper mounting brackets, and front braided lines. Lots of companies have Brembo kits for use with 17" wheels that use a floating rotor on an aluminum hat. These kits run around $2300. Replacement rotors cost over $200.
The Ultimate Garage sells a Movit brand Porsche brake kit that will fit under some 16" wheels on E28's. This is probably the finest front brake setup for the car. If you need that much brake, I'm sure it's worth the $2900 price tag. If not, it's an expensive fasion accessory.
One warning: any front brake change will add too much front brake bias that is noticeable on the street and track. When combined with stiff springs to cut nose dive under braking, the front brakes don't give the rears a chance. I finally installed the vented rears from an E34 540 and am very pleased. They bolted right up. The only modification I had to do was to the dust shields.. I had to trim back both the inner and outer lips to clear the wider rotor. The additional rear bias is noticable and welcome at the track. For you used part junkies, the E34 M5 used the same rear brakes and will bolt on the same way. For those of us on a budget, the solid rear brakes from an E34 525i are the same diameter and will do the same thing for brake bias for about half the cost. Rumor has it that the rear calipers and mounts from an E32 740i are identical and will mount up with E34 540i rotors.