The first thing you have to know is that there is no one-size-fits-all telescope. Believe me on this one — every amateur out there would love to have a single telescope that covers everything they'd ever like to do but it simply doesn't exist. It's kind of like having the one perfect lens for your camera; there are some very good general purpose zoom lenses that will do most of what you want to do, but none will ever fit every occasion. But the good news is that there are some telescopes that will cover a wide range of types of observing.
The second thing you have to know is that, like most other things, you get what you pay for. There are a few pricier brands, but the profit margin in the telescope business is nothing like it is in, say, the luxury car business where you are paying for the name. With telescopes, that name came from a history of good quality.
Since there are several buyer's guides written by amateurs or sponsored by astronomy-related companies (not of which sell telescopes), I'm not going to try to cover the whole topic. Instead, here are a few sites to get you started.
- Telescope Buyer's FAQ by Dennis Bishop, another amateur.
- How to buy a telescope: accessories, gadgets, constraints sponsored by space.com.
- Telescope Buying Guideby planetarium.net.
- The Heretic's Guide to Choosing and Buying Your First Telescope by Michael J. Edelman, another amateur.