Question: I am looking for compare utility similar for "win merge" or "beyond compare" .
That in addition for gui comparison will have api that i will be able to run on my files via my code and see if the files are the same or not and also use it in gui mode to show graphically the differences .

Any recommendations ?

thanks

Answer: 
If you're looking for a Diff API (as opposed to a standalone tool), try [DiffPlex](http://diffplex.codeplex.com/).
Check out [Araxis Merge](http://www.araxis.com/merge/index.html) - it's a two-way or three-way diff utility, it can handle ANSI, ASCII and Unicode files (it can even compare an ANSI file to a Unicode file!), and it offers both a command-line interface, as well as an [automation API](http://www.araxis.com/merge/automation_ref.html) for including its smarts into your own apps.

Highly recommended!