What should you look for in a detector?
Lets start with a few basics.
For example, how much money do you want to spend? If you're like most people new to the hobby, you want to start inexpensively (less than $300) and then go up from there if you decide you like it. But others like to dive right in and get a more expensive machine despite the learning curve. That's one you'll have to decide.
Next: where do you plan to hunt? Must people hunt on land (parks, schools, etc.), but others have the beach in mind. If you're going to the beach, most land detectors will do ok in the dry sand, but not so good (make that "lousy") in wet sand and while most coils are waterproof, you cannot get the control box wet (it isn't waterproof) so you'd best stay out of the water (rogue waves could swamp you and your detector). So if you want the beach, you ought to think about a different detector made for the beach and those are typically more expensive ($650+).
Ok, next question: what kind of detectorist are you? Are you the kind that likes to look at a screen that tells what you've likely hit (screens are accurate about 50-60% of the time) and how deep it is (depth meter accuracy is about the same), or are you the type that prefers to go off of tones only (no screen). It should be noted that you will get the tones as well on a screen machine, and some detectorists don't even pay attention to the screen because of the inherent inaccuracies. It's all up to you.
So, assuming you want to go inexpensively, I will save you some time looking through the posts and tell you this:
If you want a screen, most folks will suggest you get the Garrett Ace 250.
If you want a tone-only machine, most will suggest the Tesoro Silver uMax.
They are priced pretty evenly.
If you want a beach machine, you'll need to shop around. Again, you'll either be directed towards a multi-frequency machine (Minelab Excalibur II, $1200), or a pulse induction detector (which offers no discrimination: if it beeps, you dig) which will start around $650 new.
You can always buy used, but be careful doing that, of course.
Good luck and happy hunting!