welcome to nym! i would start with the classifieds on here. good stuff ,also might help if you post what year and motor your stang is and has. for throaty i would reccomend bassani.
First of what year are we talking about, if you're going for a throaty deep sound then you should go with an H pipe, Y pipes are generally raspier but give extra couple of horse powers. for the cat back I love the sound of flowmaster 40, or for louder sound magnapacks
Take a logical approach and ask yourself.....How loud do I want to be? or not. For me Borla gives me both nice sound when just cruising and Great RAP when I pick up the RPM's. Look, Listen and talk to other mustang owners.....you'll get there.