What would be the MBTI personality type of Sheldon Cooper?

I believe Sheldon well fits into ISTJ. From wikipedia:

Extraversion/Introversion The extraverted types learn best by talking and interacting with others. By interacting with the physical world, extraverts can process and make sense of new information. The introverted types prefer quiet reflection and privacy. Information processing occurs for introverts as they explore ideas and concepts internally.

Sensing/Intuition The second continuum reflects what a person focuses their attentions on. Sensing types enjoy a learning environment in which the material is presented in a detailed and sequential manner. Sensing types often attend to what is occurring in the present, and can move to the abstract after they have established a concrete experience. Intuitive types prefer a learning atmosphere in which an emphasis is placed on meaning and associations. Insight is valued higher than careful observation, and pattern recognition occurs naturally for Intuitive types.

Thinking/Feeling The third continuum reflects a person’s decision preferences. Thinking types desire objective truth and logical principles and are natural at deductive reasoning. Feeling types place an emphasis on issues and causes that can be personalized while they consider other people's motives.

Judging/Perceiving The fourth continuum reflects how a person regards complexity. Judging types will thrive when information is organized and structured, and they will be motivated to complete assignments in order to gain closure. Perceiving types will flourish in a flexible learning environment in which they are stimulated by new and exciting ideas. Judging types like to be on time, while perceiving types may be late and/or procrastinate.

P.S. I can relate to Sheldon very much and when I took the complete MBTI assessment, i too was categorized as ISTJ.