The file comparison works really, really well, better than a lot of expensive tools that I have tried. I keep coming back to DiffMerge even though the UI looks so simple and boring.
I sometimes use it in combination with VisualDiffer (Mac, App Store) or ExamDiff (Windows, Freeware) to get a more traditional look.

just discovered diffmerge, and it's really great. other, pricey, comparison apps probably do this to, but I like that it lets you have a whole bunch of folder comparisons open

Really great app, it's free and for the price it's much better than other commercial diff/merge apps.