Meditation is a subject close to my heart, having practiced some form of it since 1973. There are many kinds of meditation for accomplishing various things (including awakening kundalini and acquiring special abilities/powers), but in my opinion the most profound thing that meditation can reveal is what "You" are. Some people use a "sacred word"/mantra, others use visualization, some use breath awareness - the variations are many. And then there is a kind of meditation where you simply allow everything to be as it is - this is my favorite because it doesn't force the mind to do anything in particular, and the best part is that this kind of meditation can be done during activity.
A very good start for people who want something simple, easy, and effective is what Satanus suggested. A more formal approach that combines breath awareness with mantra meditation is Herbert Benson's "Relaxation Response". Another mantra style meditation that comes out of a Christian perspective is "Contemplative Prayer" as taught by Thomas Keating. His method is very much like the TM technique except you choose your own mantra (what he calls a "sacred word"). He has an excellent book called "Open Mind Open Heart" which gives you lots of guidance and background information - you can also easily find lots of things on the internet on his teaching as well, inclucing youtube vidoes.
I would caution against learning TM since it is not really upfront about a lot of things, plus it's unbelievably expensive now, somewhere around $1500 (I learned it for $35 in '73). The TM organization will focus on getting as much money out of you as they can. The meditation itself is OK, if you don't mind the Hindu overtones (which they'll deny) but the organization is cult like and has a veneration of its founder, Maharishi Mahesh Yogi, that should set off alarm bells. My advice is to stay away from it.