I know there is a thread out there somewhere on this very subject but I can't find it.
Off the top of my head:
1. Almost any five lug wheel from the newer generation. Just have to watch offsets and width as some will require spacers and or fender rolling.
2. MP3 ECU (manual only and requires premium gas to get the benefit)
3. MSP stock turbo (MSP used same 2.0 FSZE so it's a direct bolt-on)
4. MSP exhaust (will have to cut the piping from the muffler to tip off and have tip rewelded back on - I had an 03.5 on mine and loved it, great sound, only reason I sold it was I upgraded to a Thermal R&D catback)
5. MSP radio pocket and support bar (nice clean look with a single din radio...I have one.
)
6. CX-7 shorty antenna to get rid of the RC car look (others have used an S2000 antenna)
7. Mazda6 wagon rear wiper (I have this too and love it, looks better than stock and functions better too - can find the kit of everything you need at
www.onlinemazdaparts.com)
8. Tribute washer nozzles (provide a nice mist over the stock nozzles, even better it's a cheap and easy upgrade)
9. Tribute/Escape/MPV wiper stalk (variable intermittent wipers!!!! - off the top of my head I don't remember exact years but IIRC 2004 and up should work)
10. MSP bumper (direct bolt-on and gets rid of the amber bumper markers)
11. MSP lip (very hard to find these days)
12. Sedan headlights (will require some re-wiring as they are single bulb vs. the P5 dual bulb system)
13. MSP rear subframe and rear sway bar (the subframe is not needed to mount the RSB but the mounting points are a bit different from the P5 which is why most owners who upgrade to the RSB complain of the clunk)
14. Escape front end links
15. MX-6 rear strut bar (can be found on Ebay for cheap, not sure if it provides any real benefit though)
That's all I have for now.