**Disclaimer** There are a million threads about exhaust setups so I thought I would put it all together. Please add pics, videos, and specs and opinions on your setups but please don't put a bunch of questions and useless jarble. All info may not be entirely 100% accurate. Either PM me and I will edit it or just add-on below. Thanks. Moving On....
OK So you wanna upgrade your exhaust.
There are 3 different sections that are upgradeable. They are Headers/ Manifolds, Y-Pipe, and "Cat-Back" Exhaust.
Headers/ Manifolds- This is the first section of the exhaust where it exits the engine and starts its journey down the pipes. There are 2 types of upgrades.
Short Tube-have to be welded on, keep OEM O2 sensors, they are smog legal, these have decent power gains
Long Tube- direct bolt-on replacement, have to have O2 simulators, are NOT smog legal, the most power gain
Brands: Doug Thorley- long and short; JBA- only short
Summary: If you want the most power gains, get the Doug Thorley Long Headers; if you want decent power and stay fully legal, get the short headers
Y-Pipe- I don't know much about this other than to make the merging of the exhausts flow better.
URD- This is stock size with a 2.25" pipe and removes the catalytic converters.
Doug Thorley "Pipe Bomb" removes the cats and replaces with resonators.
Cat-Back Exhaust- This is the most popular exhaust upgrade and there are lots of choices out there. This replaces the entire setup behind the catalytic converters. Pretty much every setup has Mandrel Bent piping which means no pipe narrowing at the bends. This helps with reducing flow restrictions. There are 2 different styles: single-side exit and dual side exit. There are also different sized pipe depending on what performance changes you want.
Single-Side Exit 2.5" Pipe- Slightly larger than stock. You will not lose any low end HP/ Torque, but do not gain as much in the top end. I believe this size gives you the most overall power gains on a dyno test. The peformance changes of the different brands are all similar and its really a matter of which sound/ brand you want.
TRD- single welded unit, so no clamps or having to weld. Its not really much louder than stock and has a nice throaty purr.
Magnaflow, JBA, Borla, Dynomax, Gibson- sectional pieces that are clamped or can be welded. They all sound a little different. Listen to the sound clips and go from there.
Single-Side Exit 3" pipe- This will give you a small lose of HP/ Torque in the low end, but more gain in the top end. This would be good if you go into the higher rpm range more often.
Banks and URD are this size.
Dual Side Exit 2.5" Pipe- These look and sound awesome but they also lose a little power in the low end.
Flowmaster and MBRP make these.
Popularity: TRD, Flowmaster, and Magnaflow are the most popular choices for cat-backs
Muffler/ Custom setup- There are a lot of people who also just swap out the actual muffler. And there are those who make a custom setup at the local muffler shop. This tends to be $100-$200 less than a brand name full cat-back setup and they are usually happy with it.
Magnaflow and Flowmaster are the popular choices for mufflers
Regardless of the power gains/ loses, generally everybody is happy with whatever setup they get. Usually sound or fitment of a particular setup seem to be the typical reason people don't like what they chose and switched to something else. Any power loses you get from a larger exhaust should be countered by the gains of a good CAI.