I'll give a big thumbs up to the Borlas also. Specifically the Pro XS mufflers, or the slightly louder XR1s. I have Borla Ataks on my '09 GT and the Pro XS on my 427 Mach 1. I really like them both, but the Pros sound great with a healthy big block.
If you like the sound of glasspacks, you'll love those I think. They use a long woven stainless mesh instead of fiberglass packing, so they won't blow out over time. They flow better than almost any muffler out there, sound like a muffled open header design, don't drone (like Flowmasters are
notorious for), sound mellow at idle, but open up under throttle without getting that annoying raspy sound typical single pass through glasspacks get when under wide open throttle. The Pros use a split flow pipe inside the muffler, much like the Edelbrock Split Flows I bought years ago for my truck (but are no longer made I believe). The XR1s are a single pass through so they are a little louder.
Magnaflows are very popular and sound nice, but the Borlas sound a little better in my opinion. I like an aggressive sound, but can't handle drone.....it drives me insane. Size of pipe, X or H pipe...or lack of, length of tailpipe etc all affect the sound, but the basic sound is still the same.
Here's a few clips of the Borla Pro XS mufflers.
First two are a big block Mopar (but with no long tailpipes, so a little louder than typical)....
http://youtu.be/WdAv3O_JUYs?t=15shttp://youtu.be/yCCYTEzRrpo?t=27sThis one is a small block Mustang, but you can hear what a mellower setup sounds like taking off....
http://youtu.be/bU19A60K_Zo?t=1m47s3rd is a healthy stroker smallblock Mustang, again with no visible tailpipes so a little louder....
http://youtu.be/1zUocGD0-VIOnly drawback, they aren't the cheapest. But all stainless construction, lifetime warranty and USA made are big pluses.
There are tons of videos of Magnaflows. I like being the odd guy out
For the heck of it, here's a clip of the similar Edelbrock Split Flows on my truck. But headers and smaller 2 1/4" exhaust with about 6 months on the mufflers (so they have blown out quite a bit) make it a little on the raspy side. Still no drone though, and they've been on for almost 20 years now. Don't have a clip of the Mach 1.