No one telescope is perfect for all applications and many astronomers have more than one. But if you aren't sure whether astronomy is the right hobby for you, or simply want the occasional look at the sky, then it makes sense to get as much help as possible.
Seeing is believing: Well not always, but it is a good start and this is where your local astronomical society can help. You will also find lots of helpful videos at the Astronomy and Nature centre and the Stargazers Lounge Forum is THE place to go to discuss all your problems.
Most societies will have Star Parties and regular viewing sessions, weather permitting. These will give you an opportunity to see the various sorts of telescopes, their relative sizes, etc., though you may not see the cheaper, starter scopes that we have been talking about. But if you get the chance to look through the bigger scopes it will give you some idea of exactly what can be seen if you progress beyond the beginner phase. And there are all the photos which you will see on their web sites.
Astronomy tends to be a solitary occupation and at your local astronomical society you may need to be polite but persistent if you want to find out more. By far your best bet is to go to one of the Star Parties that they organise. These normally go ahead regardless of the weather as they usually have some room(s) where everyone can meet. Better still, they will often operate telescope clinics where you can take your telescope, if you have one, and discuss your problems - or see others! And if you don't have a scope, which is what we are assuming here, you can see the various types and get some idea of their sizes and how they work. And if the weather is fine you can have a look through them. Do take advantage of these opportunities.
Of course if astrophotography grabs you, then the requirements begin to change though you can, for very little extra expense get good photos with webcams. But sticking with the visual side and 'small' scopes for beginners the table below gives a very approximate guide assuming that the you use just the very bare essentials.
Oct 2014 - sorry - missing due to change of software update!
Whether you are a beginner or experienced astronomer I would very strongly recommend
'An Amateur's Guide to Observing and Imaging the Heavens' by Ian Morison, published by Cambridge University Press.
It is very up-to-date and comprehrensively covers virtually everything on
Telescopes, Binoculars, Observation and Imaging, with a final chapter on Spectroscopy.