Now, on to business:
Before you go ahead and spend roughly $2k+ on HID's and a performance chip, might I suggest the following?
1. Get an E36 M3 rear diff (for obvious LSD-related reasons)
2. Get your ECU reflashed. Does all the same things as a performance chip, but should potentially be cheaper depending on who you know.
For the future:
1. Turbocharger or supercharger. Due to being a USDM E36, your engine has iron cylinder sleeves and what I'm fairly certain is a goodly amount of deck metal. I, for one, suggest you make use of that if only for better fuel economy (in the case of the properly sized/tuned turbo route). Obviously there are many other benefits to forced induction, but that is the one you will tell the emissions people
.
2. Individual Throttle Bodies. I can't recall at the moment whether or not BMW uses ITB's on all of their I6-powered cars, but I could easily see them doing so. Either way, chances are good that they don't flow nearly as well as a set of Extrudabody 45mm ITB's. Such a setup would be most beneficial for the fore mentioned turbo route due to needing to make/buy an intake plenum and get a new air sensor anyway. Obviously not really a particularly important modification unless you want to get the absolute most power out of your engine after having taken care of just about anything else, unless you really like the cool looks of exposed inline throttle bodies
.
3. M3 6 speed swap? Probably plenty of crashed E36 M3's in the junkyards to look through
.
Once again, great car!
~ Scott