My name is Marie and I am an INFJ.
If you want to take the test to find out what you are (and yes, I know you can't fit into just one category, all you Ps), here is the most accurate one I have found that's free. It's still not right 100% of the time, but who is (except me, of course, so if have any questions about who you are, just ask) ? Then after you know your type, this is the site you go to to read about it. It has the best descriptions of all the pages that I have found. It is also gaggingly aggrandizing, so I have included a list of jokes that all pretty much fit as well. I got them from here and here and here and here (though the funniest one, this one switched the ENTJ, INTJ, and INTP they should be each others'). These pages are hilarious if you know the types well.

The jokes first:
Illusions of the Unhealthy XXXX by Doug Bates
INFJ - "I have the best intentions"

If we were cats
INFJ="Skitty Kitty": Wants to be affectionate, but never quite overcomes nervousness. "Intrepid" is NOT her middle name. Likes to watch the proceedings from a safe spot, such as the top of the staircase.

Negative MB Type Descriptions by Hal Dendurent
INFJ: "Messiah": Characterized by the burning desire to change the world, which desperately needs everyone to be NF.

Asking the Myers-Briggs type if the water is half-full or half-empty:
INFJ - (closes eyes, concentrates) It's half-empty. (The INFJ is referring to a glass that is 200 miles away)

INFJ
You are a geek. In grade school you sat in front, never spoke unless called upon, but always got straight A's anyway. In high school people cheated off your tests and you let them. Then they stole your lunch money.

Pompous description from personalitypage

Only one percent of the population has an INFJ Personality Type, making it the most rare of all the types.
INFJs place great importance on having things orderly and systematic in their outer world. They put a lot of energy into identifying the best system for getting things done, and constantly define and re-define the priorities in their lives. On the other hand, INFJs operate within themselves on an intuitive basis which is entirely spontaneous. They know things intuitively, without being able to pinpoint why, and without detailed knowledge of the subject at hand. They are usually right, and they usually know it. Consequently, INFJs put a tremendous amount of faith into their instincts and intuitions. This is something of a conflict between the inner and outer worlds, and may result in the INFJ not being as organized as other Judging types tend to be. Or we may see some signs of disarray in an otherwise orderly tendency, such as a consistently messy desk.
INFJs have uncanny insight into people and situations. They get "feelings" about things and intuitively understand them. As an extreme example, some INFJs report experiences of a psychic nature, such as getting strong feelings about there being a problem with a loved one, and discovering later that they were in a car accident. This is the sort of thing that other types may scorn and scoff at, and the INFJ themself does not really understand their intuition at a level which can be verbalized. Consequently, most INFJs are protective of their inner selves, sharing only what they choose to share when they choose to share it. They are deep, complex individuals, who are quite private and typically difficult to understand. INFJs hold back part of themselves, and can be secretive.
But the INFJ is as genuinely warm as they are complex. INFJs hold a special place in the heart of people who they are close to, who are able to see their special gifts and depth of caring. INFJs are concerned for people's feelings, and try to be gentle to avoid hurting anyone. They are very sensitive to conflict, and cannot tolerate it very well. Situations which are charged with conflict may drive the normally peaceful INFJ into a state of agitation or charged anger. They may tend to internalize conflict into their bodies, and experience health problems when under a lot of stress.
Because the INFJ has such strong intuitive capabilities, they trust their own instincts above all else. This may result in an INFJ stubbornness and tendency to ignore other people's opinions. They believe that they're right. On the other hand, INFJ is a perfectionist who doubts that they are living up to their full potential. INFJs are rarely at complete peace with themselves - there's always something else they should be doing to improve themselves and the world around them. They believe in constant growth, and don't often take time to revel in their accomplishments. They have strong value systems, and need to live their lives in accordance with what they feel is right. In deference to the Feeling aspect of their personalities, INFJs are in some ways gentle and easy going. Conversely, they have very high expectations of themselves, and frequently of their families. They don't believe in compromising their ideals.
INFJ is a natural nurturer; patient, devoted and protective. They make loving parents and usually have strong bonds with their offspring. They have high expectations of their children, and push them to be the best that they can be. This can sometimes manifest itself in the INFJ being hard-nosed and stubborn. But generally, children of an INFJ get devoted and sincere parental guidance, combined with deep caring.
In the workplace, the INFJ usually shows up in areas where they can be creative and somewhat independent. They have a natural affinity for art, and many excel in the sciences, where they make use of their intuition. INFJs can also be found in service-oriented professions. They are not good at dealing with minutia or very detailed tasks. The INFJ will either avoid such things, or else go to the other extreme and become enveloped in the details to the extent that they can no longer see the big picture. An INFJ who has gone the route of becoming meticulous about details may be highly critical of other individuals who are not.
The INFJ individual is gifted in ways that other types are not. Life is not necessarily easy for the INFJ, but they are capable of great depth of feeling and personal achievement.

For those ENTPs out there he kind-of gives you a bad name.