The equipment from Racing Beat is top notch. I have bought the cold-air intake (K & N), the sway-bars, end-links, springs, and exhaust from Racing Beat. I also installed a K & N oil filter and run Royal Purple Synthetic motor oil. NGK Spark plugs. New brake system: CorkSport steel brake lines, Hawk HPS brake pads, Brembo front and rear rotors, and Brembo brake fluid. CorkSport also offers great products. I bought exhaust hangers from them to go with my RB mufflers, as well as a low-pro antenna, rear camber arms and Atenza badges. The last site I recommend for other random goodies is Street Unit. Prices aren't low, but you get what you pay for when it comes to car parts. You can look for a lighter battery (Optima perhaps) and remove the spare tire and its accessories to lose some weight, but of course that leaves the chance of a flat you can't fix! My last recommendation is if you want to go for a unique, but still somewhat factory look try to find the Racing Hart wheels made for the old Mazdaspeed Protege.
Mazda's aren't HP monsters, but with smart tuning you can make your 6 handle like a large Miata and Zoom-Zoom!
2004 Mazda6 Sport Wagon