CompareIt! [1] - It's an ancient diff program last updated over a decade ago, but I've never found a diff program nearly as useful.
It is windows only, but it is fast, allows quickly setting manual anchor points (I miss this horribly when doing git diffs via vimdiff), and has converters for common file formats like doc and pdf (extracts the text and then does the diff).
I use it for both work and home. In addition to code diff, it's great for comparing things like PDFs of insurance renewals, to see what has changed.
It's the best $30 I've ever spent on software.