General rules of thumb:
Ignore claims of magnification this is determined by the eyepiece what is important is the diameter of the lens or mirror (how much light it can grab)
Secondly how good is the mirror or lenses - cheaper mirrors tend to be ground to a spherical shape and will suffer to some extent from what is called spherical aberation better quality mirrors are parabolic in shape and produce a much better sharper image.
Thirdly the mount is important. You'll want what is called an equatorial mount - preferably motorised. This means that as the object crosses the sky it's easy to keep track of it. This is especially important if you want to be able to take photographs through it at a later stage. Astronomical photographs take a very long time and the better the mount and drive the better result.
As ever you have to pay for quality but paying more money doesn't always guarantee it.
Have a look at some of the telescopes here:
http://www.telescopes-direct.com/
You certainly get more for you money now than when I first bought a telescope 30 years ago