Glass packs.
A glass pack or dual glasspacks on a V8 sound awesome. I put a pair of glasspacks on my header'd 79 camaro, and it sounded totally awesome. I also have a glasspack on my truck, which has stock manifolds and a Y pipe leading to the glass pack, it sounds pretty good too. Glasspacks are great for giving you a deep, bass rumble but keeping down the noise to an acceptable amount. Both my vehicles have a very quiet, distinctive, bass idle that you can definately hear but isn't loud enough to attract attention from the police. When you rev it little, it makes a nice growl, almost a bark, and when you gun it roars. What I like best is the way it growls when you push in the clutch at the same time you let up on the gas (not letting up first, as one may often do).
I wish I had a nickel for everytime I pulled up to a light with my truck and had the guy next to me ask what I had for a motor. I've even heard guys betting eachother I have a big block when I leave it idling at gas stations.