REFRACTORS are the most commonly available type. Many people think of them as being "real" telescopes, because they most resemble the classic spyglass ("Arrgh, mateys! There be a French brig off the larboard bow") But refractors are very expensive, which accounts for the very small size of most available for sale. There is nothing very wrong with "department-store" telescopes, like Tasco or Jason, but there is very little right with them either. They generally have cheap eyepieces and wobbly mountings (both easily cured by spending more money), but there is no remedy for their miniscule size. Serious astronomical refractors (4-inch lenses and up) cost thousands of dollars.
CATADIOPTRICS are generally of the Cassegrainian configuration. That means they have a window or a lightly curved lens on the front and a mirror in the back. In the center of the front window is a smaller secondary mirror. The net effect is to fold the telescope up so that it is much shorter than the focal length. Common models of astronomical "cats" are Celestron and Meade 8-inch Schmidt-Cassegrainians, with a minimum price of about $1000. With options this can go through the stratosphere.
REFLECTORS for amateurs are usually Newtonian reflectors. These are the least expensive quality telescope, and is what we recommend. The downside is that you have to fiddle with them more to keep them aligned. In a way, this is an advantage because it forces you to understand your telescope better, and when you understand them you can get more out of them. About $500 gets you a nice 6-inch f/8 reflector in the Dobsonian configuration (manufacturers: Meade, Orion, and Celestron). The Dobson mount is a very stable trunnion mounting.
UNITIZED GO-TO SYSTEMS are a new feature of the telescope market. They appear in all three of the above categories and are mounted on a drive system with automatic stepper motors. The best of these, in my opinion, are the catadioptrics. The refractors are universally too short (view them as a self-pointing low-power monocular).
If you want more information about buying telescopes, go to this remote page. The author is respected reviewer Ed Ting, and the article gives tons of great advice. Be sure to visit his review page also.
join an amateur astronomy club. People tend to get a telescope long before they really need one. In fact, we advise you to get binoculars and a few astronomy books now, join the club, and see if you are still interested in astronomy next year. If you're not, the binoculars are still useful. If you are, you will be able to select a telescope more useful to the type of observing you like.