Research-minded analysis of the Enneagram, especially in the context of the author's MOTIV system and his statistical approach to validating personality classification systems.

Accurate, thorough descriptions of each MBTI personality type.

Turns out I'm terrible at this! Who knew?

Extensive Meyers-Briggs personality test, with Enneagrams tossed in for fun.

Wikiversity userpage with an overview of behavioral psychology concepts

One of my favorite pages on Wikipedia -- this describes a way to look at MBTI types that highlights interaction styles and temperaments. Has strong parallels to the Insights Discovery evaluation.

large list of personality tests, including MBTI

This has solid advice on INTP growth. Develop your extraverted intuition; learn to see things objectively.

Bronxelf totally pegs it: the internet lets introverts interact with people on their own terms.