Like lots of other people I have come to like latexdiff to highlight changes between versions of latex documents. It takes two latex files as input and outputs a new latex file, in which changes are highlighted. I use a lot of pgf/tikz for graphics and latexdiff will destroy tikzpicture code. To avoid that I call latexdiff as (the hint how to do this came from stackexchange):

latexdiff -c PICTUREENV='(?:picture|tikzpicture|DIFnomarkup)[\\w\\d*@]*' VersionBefore.tex VersionAfter.tex > Diff.tex