I’ve used FileMerge (OS X) as a nice visual diff, but until this week I hadn’t used it for merging files. Now I have, and it’s wonderful for merging files. You do all the work with the arrow keys. Up and down arrows jump to the previous or next difference. Left and right arrows pick the version you prefer for each difference. Then at the end, you save the merged file. It saved me a lot of time when I clumsily saved over something and only had a stale backup.