A, C, D, E, G are the five Major chords you will want to learn first.. not necessarily in that order. Many people learn E, A and D first.. since that is used in so many songs.. but the open C Major and G Major chords have such big, resonating sounds that they used in a lot of acoustic stuff.. every style has it's "common" chords of course but definitely learning these five to start with is a good idea. The most common minor open chords that I come across are A minor and E minor. So they would be a good idea to learn too.. the other chords can be learnt as you go... I forget exactly how many possible chords there are.. but it's in the billions.. 17 billion.. or may be 1.7 billion.. I can't recall exactly.. but what I do remember is laughing out loud when I read it. :p

No need to freak out though.. like I said.. there are only about a dozen chords that get used frequently and those seven I mentioned above are the most common. Do what Benoit said as well.. learn a scale or two or three..