I love disc brakes. I took a 2002 Trek Alpha 4500 with the goal of making a raceworthy hardtail bike, and I knew that disc brakes were a must. I love making wheels, so I laced my own front and rear wheels to my own specifications. Making your own wheels is a big undertaking if you're new at it, and since you want to make sure the disc wheels are strong, your best bet is to buy them.
Now, there are two main kinds of disc brake hubs. The standard Six-Bolt Hub and the Center Lock Hub. The Six-Bolt Hub is the one I recommend. Brake calipers often are packaged with six-bolt rotors (the disc part of the disc brake). Based on the size of the rotors (I recommend 160mm for both for your style of riding), you will likely have to get a mounting bracket or an adapter so the calipers will attach properly to your frame.
I rebuilt my Trek with an Avid BB7 mechanical rear disc brake and a Hayes HFX hydraulic front disc brake. Based on my experiences, I advise against getting Hayes.
The Avid BB7s are great as far as mechanical disc brakes go: You can adjust the brake pads on either side of the rotor and get the braking power you need, and since it's not absolutely necessary to have full housing on mechanical disc brakes, you do not have to alter the cable stops on your bike frame in order to convert to disc brakes. You would have to alter the cable stops if you were to switch to hydros.
Disc brakes are far better than rim brakes in wet conditions and dusty conditions. The drawback is that your bike will look flashier, and if you don't bring it indoors with you or lock it up in a safe place, it may disappear when you leave it unattended.