For many beginning astronomers, the mount the telescope sits on is often, erroneously, an afterthought. Bottom line: the mount can make or break the observing experience whether it be through merely being too small or simply not having the desired functionality. Telescope mounts fall into three main categories, each of which will be examined.
Equatorial. The equatorial mount, while being initially difficult to use for a beginner, is the type of mount prized by the most serious of astronomers. Operating on a dual axis design, the equatorial mount can, when equipped with a motor drive, track the stars as they move across the sky during the course of a night. For this reason alone, it is the choice of the serious observer and the only choice for any astrophotographer more advanced than tripod photography. Another plus of the equatorial mount is that it will come equipped with slow motion controls, which allow for manual adjustment of the telescope in the most minute motions to compensate for Earth's rotation without the use of a motor drive. The only real down side of this mount design is that it can be just about impossible to point the telescope close to the North Celestial Pole.
Alt-Az. An abbreviation for “altitude-azimuth,” the alt-az. mount is a simple point and look affair. For the beginner, this is perhaps the most user-friendly mount on the market as it is, without doubt, the most intuitive in use, simply grab, aim, and look. For serious observers who want a second, often portable mount, a small mount of this design is often the preferred choice. Like the equatorial, the alt-az can come equipped with slow motion controls. Unfortunately, unlike on an equatorial where hand-controlled tracking can be done by turning one knob if polar alignment is true, no such thing can be done on an alt-az as you'll find yourself working both knobs simultaneously for the simple reason that the mount can't align with your latitude. Also, look out for your tripod legs when aiming.
Dobsonian. The simplest of all telescope mounts, the Dobsonian is essentially an alt-az using a lazy susan rather than a tripod and mount head design. First popularized by John Dobson in the 1980s, the Dobsonian has become the mount choice for large reflectors in recent years thanks to its simple design, low cost, and the fact that it sits low to the ground, thus eliminating the need for step stools to get to the eyepiece. On the down side, the Dobsonian has no slow motion controls and can be quite a pain to aim when trying to view near zenith. Still, just by looking how most reflector rigs are sold today will leave no doubt in one's mind that the Dobsonian is immensely popular.