Magnaflow:
Domestic Cars (Ford, Chevy, some Pontiac)
Sport Compact (Acura, Honda,Ford, Mazda, others)
Trucks (Ford, Chevy, Jeep, Nissan, others)

Flowmaster:
Flowmaster Audio Page (Most domestics, some imports)

Dynomax:
Dynomax Audio Page (Some domestics, few imports)

Spin Tech:
SpinTech Media Page (Only common domestics)

Audio is a great place to start in your search for finding the right sound for your vehicle, however sound may vary from vehicle to vehicle depending on modifications.