Geez... I've been using *NIX for 20 years, and I never knew that the diff command had an option to show the difference of files side-by-side. Normally when you diff a file, you get to see all the differences with line numbers and > and < symbols to indicate addition and deletion of content. But if you add the -y command to diff, like diff -y, then it shows both files side-by-side and it makes it *way* easier to see the differences.

You can also use this flag when performing diffs in CVS like so: diff -y -r version_1 -r version_2 file_name and it will also show the differences between the versions of the file in side-by-side mode.

This has completely changed my life for the better :)