Myers-Briggs?
The Myers-Briggs Type Indicator (MBTI) is a test used in psychological fields to measure how people perceive the world.

Traits
The following are the traits used to describe people:
~ Introverted vs Extroverted
~ iNtuition vs Sensing
~ Thinking vs Feeling
~ Judging vs Perceiving

In each of those 4 categories, you will have one trait that is higher than the other; which will result in a four-lettered shortcut that describes your personality. Some examples could be INTJ, ISTP, ENFP, ESTP.



Characteristics
Introversion vs Extroversion: Many people think that being introverted means that you always sit by yourself and never talk. Fact is that "being introverted" really means that you need time for yourself to recharge; unlike the Extroverts who need pretty much constant action to get energized and would simply go nuts if they don't get their "social interactions".
Also "talking much" does not necessarily mean that a person is an Extrovert. Introverts can talk a lot, especially if you ask them about the right topic. Plus they CAN stand to be social for a while, but sooner or later they will have to be by themselves again to recharge, because people (or constant action) tends to drain them. Extroverts however can be around action for days and end up being even more energized than before. That is the big difference.
To put it very simple, Extroverts tend to be "Action, Action, Action", while Introverts are more of "Action, Break, Action, Break".
Introversion and Extroversion is probably the hardest to tell, when typing people. It is very easy to be off on this one.

iNtuition vs Sensing: Sensors are more likely to grasp the "little details" in the world, because they are interested in them. They often also like to stick to rules and common ways to fix / do things. Intuitives are more of "I am somehow gonna manage that" persons. They fix problems very creatively and sometimes people wonder about their "strange" methods.
Also, Ss like to use their senses and are less likely to question things, while Ns like to question and pick stuff apart (seeing different meanings and possibilities).

Thinking vs Feeling: There is not really much to say about this. Thinkers solve problems more with "what makes sense" (which is decided in the mind); while Feelers will consider their (and maybe others) feelings.
In very extreme cases, Thinkers tend to "lock their feelings up", because they think that they "don't make sense" (especially if they seem random).

Judging vs Perceiving: Judgers are the organized, ahead-planning people. They live in the future, to say so. Perceivers are more chaotic and spontaneous.



Tests
A test I personally like is the Kisa-MBTI-Test, just because you have 3 options (yes, no, in between), which makes the test more accurate in my eyes. Feel free to check it out.
~ Kisa Personality Test (46 quick questions)

You might also want to use the test from MyPersonality. You will need to sign up (it's free), but you will get a nice statistic you can use on websites and forums. You can also test your "Intelligences" (see example below).
~ MyPersonality.info Test (76 quick questions)