The latest in my exhaust evolution...
I replaced my y-pipe with a custom H-pipe. They cut out the y-pipe a bit after the cats and put in straight pipes (with a slight bend after the cats to line up with the rear). Then, just foward of the middle of the cut, they put in a crossover.
Here's a video with a few revs and a take-off (this is pre-s/c)
http://www.transcendingtouch.com/mustang/mustang3.mp4
It was $150 for the installation and the lad took his time, doing a beautiful job.