From Amjith Ramanujam :
I recently started using exclusively Vim (and gVim) for my coding needs. Vimdiff is a tool that comes bundled with Vim and its a wonderful tool for comparing code and merging changes. If you’d prefer to use a non-Vim based diff tool, checkout visual diff tools in linux for more variety. read more
Using VIM, even on Microsoft Windows, for comparing two text files is very very simple and easy to do. Definitely go check out Amjith’s post for the keyboard short cuts!