Well if you want a deeper sound with a considerable amount of power gain you can always either purchase test pipes or gut the cats. (saves your monre $$$)
Mine still has the stock calsonic exhaust with test pipes, inen CAI, and a kinetix V+ kevlar upper plenum. Compared to stock it sounds nice and deep and gives the infamous "drone" sound a nicer note. Although seeing that you have the 07 model you have the HR motor which already has a good plenum set up as it is, my suggestion is to just throw on dual pop chargers on there or K&N filters.
Here's the site where i got most of my stuff from. Really good prices and they ship out real quick.
http://hopupracing.com/nissan350z.html