since your new at this, let me give you the basic stuff you wanna know:
cat converter - you need it to be emission legal. if you decide to cut it off, it might free up a bit of hp. but, it will screw up your computer unless you install a dummy o2 sensor.
headers - replacing this with an aftermarket piece will be one of the best mod you will do to your truck. prepare to spend about $300. jba makes a decent set.
cat back exhaust - a kit that replaces your system from the cat to the tailpipe. it's made with a mandrel bent pipes (same diameter thoughout the bends) which produces more hp. some even come in stainless steel which last a lot longer. only down side is they dont usually fit well on lowered trucks.
muffler - a cheap but effective exhaust upgrade. factory muffler is very restrictive, not to mention very large. buying the muffler and getting your pipes bent is the way to go if your on a budget.
in case you wanna know i have a flowmaster 40 series single in dual out mufller, with two pipes comming out the rear bumper.
The best thing to do is:
Go to a good muffler shop. Ask the guy to let you hear different mufflers on your truck. What he'll do is cut of the stock muffler then place different new mufflers in its place with tape and rags to hold it. The the guy will rev the engine through the different sounds each muffler will make. You just stand near the truck listening to each one.
You are the only one who knows what sound your looking for, so you judge them.
And remember, the loudest sounding muffler isn't always the best sounding muffler.
The exhuast guy will let you know what's legal.
Before you do this find a very good shop, chose one that does a lot of trucks and SUVs. Stay away from RICE shops. Remember when you do this, they're going to cut off your stock muffler, so be ready to pick and buy a new muffler that day.