Say NO to straight-pipes
Don't get straight pipes. I had it done for about a year in regret to this day. Yes, is was extremely loud. But thats where the benefits stopped. As a matter of fact, it wasn't even a 'good loud' but more of a WTF is that horrible noise' kind of loud. If you have a V8 engine, you could probably get away with it, but not in our bonnevilles.
Straight pipes will cause a lot of backfire (like little gunshot/firecracker noises) especially when you release your throttle after acceleration. The faster, more aggressive acceleration, the louder more crappy sounding backfire. I also had backpressure issues, and the whole system started running too hot. CAT started smelling like rotting eggs (I never put a high-flow CAT on there like I should have).
I've put on Flowmaster 40 Series Delta Flows on my car a few years ago because I couldn't stand the straightpipes anymore. The 40 Series Delta Flows give a nice growly tone, and has a deep sounding idle (you can feel it in your chest when you stand behind the car, but its not too loud). It'* nothing like a V8, but its a nice sound still. I'm always trying to find a deeper rumble for my car, lol. Look for my thread asking about another muffler for the '00+ Bonnies.