I've been thinking about doing some minor mods to my '89 325i. Can you guys give any reccommendations for best intake, free flow exhaust, and chip? As far as brakes, I was thinking about ATE power discs and Metalmaster pads. How much of an improvement would I see with those? Also, if I wanted to go with larger wheels, what would be a good tire size with 15" or 16"s that aren't likely to cause problems with offset or rubbing? Any feedback would be appreciated.

Metalmasters are fine if you don't mind occasional noise and the only real improvement is fade resistance during 'aggressive' [hard] driving which is tough to do on the streets, I'd avoid the 'Power Discs', then tend to warp quickly.
The free flow exhaust and air filter, and a chip will probably give you the most 'bag for your buck'................Have Fun ! !

i agree with jeffrey, also headers are a nice 8 hp mod

i agree with jeffrey, also headers are a nice 8 hp mod

I know that Supersprint makes headers for E30s, but are they street legal? Also, what would be the best cat. back exhaust, as far as the biggest gains and not really worrying about noise level?

I'd avoid the 'Power Discs', then tend to warp quickly.

In that case, can you recommend a good slotted rotor?

Technically, [letter of the law], any change in the exhaust from the Cat. Conv. forward to the engine is NOT legal, though some I think have passed CA. emission approval requirements.
You might check bavauto.com to start with.

turnermotorsports.com has a nice set of headers. exhaust i like the remus.