File comparison app

[Domo]

Hi - I need one of these, and quick! Free preferably. Suggestions welcome!
(to clarify I have 2 similar files which I need to compare side-by-side).

 

[Domo]

Thanks for the suggestions guys, in the end went for Notepad++ and downloaded the compare plug-in. Works brilliantly! I have used ++ before but never knew such a plug-in existed!