At one time or another I am sure you have come across two text files that you were trying to compare the differences with like two program with thousands of lines of code.
ExamDiff is the file comparison tool best suited for this purpose. The list of features is pretty long and you will find that it is fully customizable. One of the helpful options is the ability to choose what color the changes are highlighted with so that they really stand out.
They also offer ExamDiff Pro which has a few really great features. The most useful thing in the professional version is the ability to directly edit the files within the comparison screen.
However, if you know of any other good (and free) file comparison utilities then do let us know.