Presto, for Windows developers there is a mighty fine free solution from PrestoSoft:
Typical multi-hundred line diff result
As noted ExamDiff handles diffs for files with hundreds of lines of code almost instantaneously. As users pass into thousands of lines of code and multiple files they may want to upgrade to ExamDiff Pro which is well worth the price of $35US for the time saved in larger systems. What makes ExamDiff so handy is that it can compare just about any text file in different directories, invoke an editor of your choice to update the file in either Window pane, and quickly jump from each difference point in the two files. In short a visual Diff the way you would implement it. Highly recommended.