You should be able to go to some of the manufacturers websites to get some good sound clips?

I've heard good things about Magnaflow in the last couple years. I may be switching to them for my bird as they have a shorter muffler that will fit better when I run up and over and out the back... (last owner left it at turndowns before the axle)

http://www.magnaflow.com/
http://www.flowmastermufflers.com/index.php?cat=1