We have a lot of spreadsheets (xls) in our source code repository. These are usually edited with gnumeric or openoffice.org, and are mostly used to populate databases for u
There is a library daff (short for data diff) which helps in comparing tables, producing a summary of their diffs, and using such a summary as a patch file.
It is written in Haxe, so it can be compiled in major languages.
I have made an Excel Diff Tool in Javascript with help of this library. It works well with numbers & small strings but the output is not ideal for long strings (e.g. a long sentence with with minor character change).