As I mention around here from time to time, one of my sidelines is amateur astronomy. I often get asked for telescope recommendations, so in that spirit, I wanted to put up some details in case anyone out there is thinking about one as a gift this year.
The key thing to remember with telescopes is that other things being equal, aperture wins out, because you will be able to see more objects and more details. Other things are not always equal, naturally, but that's the background of the various disputes between amateur astronomers about which kind of scope is best. And keep in mind that while a bigger scope can show you more, the best telescope is the one that you'll actually haul out and use. Overbuying has not been my problem, dang it all, but it has been known to happen. Overall, I'd say a six-inch aperture should be the starting point, although opinions vary on that, too.
You've basically got three kinds of scopes to consider: refractors, reflectors, and folded-path. The refractors are the classic lens-in-the-front types. They can provide very nice views, especially of the planets and other brighter objects. Many planetary observers swear by them. But per inch of aperture, they're the most expensive, especially since for good views you have to spring for high-end optics to keep from having rainbow fringes around everything. I can't recommend a refractor for a first scope, for these reasons. That's especially true since a lot of the refractors you see for sale out there are of the cheap/nearly worthless variety - a casual buyer would be appalled at the price tag for a decent one. No large refractors have been built for astronomical research since well before World War II.
Reflectors are variations on Isaac Newton's design, which was: open tube at the top, mirror at the bottom, and you look through the eyepiece in the side, after the light reflects back off an angled secondary mirror. All modern large-aperture research telescopes are some variety of reflector. They provide the most aperture per dollar, especially with a simple "Dobsonian" mount (more on mounts in a minute). They do have to be aligned (collimated) when you first get them, and every so often afterwards, to make sure the mirrors are all working together. A badly collimated reflector will provide ugly views indeed, but it's at least easy to fix. And if the primary mirror is of poor quality, you're also in trouble, but the average these days is actually quite good.
Finally, the folded-path (catadioptric) types (Schmidt-Cassegrain
and Maksutov designs, mostly) are a hybrid. There's a mirror in the back, but also a corrector lens plate covering the front. The light path ends up coming out the back of the tube, through a hole in the primary mirror. Like refractors, these basically never have to be aligned, but they're fairly expensive (although nowhere near as bad as refractors when you start going up in size). And their views are pretty good, although purists argue about how they compare to a reflector of equal size. (Refractor owners would probably win that argument, but they have to drop out at about the five or six-inch mark, when the other two telescope designs are just getting started). One nice thing about a scope of this kind is that it's more compact, making it an easier design to mount.
And that brings up the next topic: what you do mount one of these fine optical tubes on, so you can use them to actually look at things? An equatorial or a fork mount will let you follow the motion of the objects in the sky easily, especially with a motor drive - the Earth's rotation is always sweeping things out of your view, otherwise. A decent mount of this kind will definitely add to your costs, though. The "Dobsonian" mount is a favorite of reflector owners, since it's quite simple and allows you to put more of your money into the optics. You do have to manually grab the telescope tube and move it, though, which takes some practice (and sometimes some home-brew messing around with the mount). Some people don't mind this, others are driven nuts by it. You can put a motorized platform under a Dobsonian (my own setup) to motor-drive it, which some consider the best of both worlds.
On the topic of motorized telescope mounts, I should say something about "Go-to" models. These are not only motorized to track objects, they will slew the scope around to find objects from a database. I'm very much of two minds on these. For an experienced observer, an astrophotographer, or a researcher, they can be an indispensable tool to spend more time observing and less time hunting around. For a total beginner, they can ease a lot of frustration when first learning the sky. But at the same time, they also can keep someone from learning the sky at all, and they can also encourage hopping too quickly from one object to another. If you do that, you can see all sorts of stuff in one evening, while at the same time hardly seeing anything at all.
Visual observing is all about training yourself to see things. One thing every new telescope owner should know is that Very Little Ever Looks Like the Photographs. Especially since the photos are long exposures on wildly sensitive CCD chips, through huge instruments, and under excellent conditions. Through the eyepiece, nebulae are not tapestries of red, pink, green, and purple: they range from greenish grey to bluish grey. And although with practice you'll pick up really surprising and beautiful amounts of detail in deep-sky objects, at first, everything can look like a blob. Or a smear. Or not appear to even be there at all, even when a practiced observer can see it right smack in the center of the eyepiece field. I really enjoy seeing these things with my own eyes, and trying to find out just how much detail I can pick out and how faint I can go, but it's not for everyone.
Now, photography is another story. Astrophotography is an expensive word, although thanks to webcams and the like, getting into it is not quite as bad as it used to be. But for most purposes, you'll need one of those motorized mounts that'll track objects across the sky. That's very convenient for visual observing, too, naturally, but a really good one for long-exposure photography can cost more than the telescope itself! A motorized platform is almost never accurate enough for these purposes, I should add. I'm not an astrophotographer myself, so I won't go into great detail, but if you want to try this part of the hobby out (or know someone who does), prepare to think about the telescope mount as much as you think about the optics. As you'd imagine, all astrophotography these days is digital, with equipment ranging from simple webcams all the way up to stuff that easily costs as much as a new car, or perhaps a small house.
So, what to buy? I've scattered some Amazon links in the above to representative scopes. In general, Meade and Celestron are the two brands you'll see the most, and if you stay away from their cheap refractors, you should be fine. And Orion also sells good stuff of their own brand (On Amazonand from their own site). (Again, I'd stay away from inexpensive refractors there, too). Other good sources are Astronomics and Anacortes.
Update: as pointed out in the comments, an excellent resource for specific opinions on different models, and telescope advice in general, is Scopereviews. Cloudy Nights is also a huge resource.