As stated above there are three basic factors that contribute to clarity: process, fining agents, and time.
1) process: there is no substitute for proper hot and cold breaks. Much of the traditional brewing process has been built around creating these "breaks" and removing the resulting material. it is possible to make good beer without these traditional steps....and many here will call some of the steps "myths"....but removing the material via "process" can reduce the need for products and time. In particular many will suggest pouring everything from your brew pot into the fermenter...but that will slow fermentation, and require more time for everything to settle out of suspension.
2) irish Moss is cheap, easy, and works. Other products mentioned also work. Clarity-Ferm has not been mentioned here, it is a bit more expensive at $2 per batch, but when used properly makes a huge difference.
3)Time and gravity are your friend! Time will allow all those heavy particles to settle out during fermentation, secondary or lagering, and in the bottle. The more "stuff" left from 1 & 2...the more time needed for gravity to do the work.
There are many ways to make good beer...choose the methods that work for you. My personal preference is to focus on a good vigorous boil, irish moss, and a rapid cool to create a cold break....then leaving most of that mess in the pot. Yes...I lose a little wort volume, but I believe it is worth it.