Sway Bars
Just as the name refers, each of the four corners in an independent suspension acts on its own. As you turn in, one corner will experience more load than the other resulting in body roll. A sway bar connects the two opposite sides (left and right) of the suspension and acts as a torsion spring. This limits the action one side sees in relation to the other. In the most simplistic terms, one side of your suspension goes up, the other side will pull in relation to it, keeping weight transfer in a controlled state and reducing body roll.
Arms And Rods
As we mentioned before, the arms are what connect the upright (or knuckle) to the body. Each one of these arms has a function directly correlated to caster, camber or toe. Since the factory has to make these parts for mass production vehicles, the amount of adjustability and strength is pretty limited.
Over the past 10 years, options for these parts have made leaps and bounds. Circa 1999, if you were rolling on springs, Tokico blue shocks and a sway bar you were the man. Now there are all kinds of options to choose from. But understanding what to buy out of need is quite different than buying out of want. Take for example TEIN coilover shocks for CT9A Evolution. There are five different grades to choose from. What is the difference between these setups besides the price? The answer is that each is designed with a different purpose in mind.
So the first thing to really determine is what is going to be the main purpose of your build; whether that be spirited street driving, canyon/circuit attack, drifting, rally or drag racing. Since each one of these disciplines put a different type of strain on the vehicle dynamics, they require different settings and needs. Contrary to what you read on the message boards, no one setup is almighty. This is because how the alignment settings directly affects how the car will react.
The next step is to determine what tire you are going to run. But wait a minute, this story is about suspension. Since the tires are in direct contact with the ground, how they perform is directly related to how the suspension is setup. The control factor is the amount of grip your tires can optimally handle. This is why most manufacturers, like HKS, TEIN and Cusco, make varying grades of suspension. During development, they determine a general intended use for the suspension and tune in a range that is suitable according to a base tire. Most street level coilovers are optimally set for a high grip street tire, (ie Neova, R1-R, RS-3, etc...). Whereas competition level suspension parts are set aggressively for specialized tires such as circuit r-compounds or rally nobs. Overdoing your suspension will eat up your tires, and underdoing it will prevent you from taking the tires to its peak performance.
Street
If you aren't really planning on hammering on your car and are more interested in a nice ride, then springs and a shock combo are your best friend. But don't go with just any set of springs off of eBay. Most manufacturers of lowering springs engineer them to give you the maximum of lowering without adversely affecting the ride and reliability of your shocks. For those seeking a little more adjustability, many manufacturers have started designing entry level coilovers intended for daily driving comfort, yet have limited adjustability. In conjunction, it's a good idea to invest in a camber adjuster to maximize tire wear.