Actually, larger (more-than-two-variable) truth tables are pretty easy to make, but as the math guru who taught this to me said, it will make your arms hurt a bit. Here's how to make larger truth tables:

A truth table will always have *2^n* lines (ie, 2^n different combinations), where n is the number of variables. Thus 2-variable truth table will have 4 lines, 3-variable table will have 8 lines, 4-variable table will have 16 lines and so on. I've made a 6-variable table (64 lines) once, on paper - that was pretty boring. =)

How to fill the columns? First column will have *half* of the table True and other half False; Second will have *one-fourth* (half of previous) True, False, True, False, Third will have *one-eighth*, and so on. Final column will thus look like "T,F,T,F,T,F..." then.

Example:

A B C Op...
---------------
T T T
T T F
T F T
T F F
F T T
F T F
F F T
F F F

For three variables, table will have 8 lines; Half of it is 4, so for A there's 4 Trues and four Falses, For B there's 8/4=2 T's, then 2 F's, and so on.