Easy to compare both single files as well as a folder of files. Easy to setup. Accomodates large files easily. Presents the results in an easy graphical way to spot differences. A "must have" for any developer or administratos.

As a software developer, comparing files is a daily activity. It will suffice to say that I have settled for beyond compare (3.0) to do that for me for the past 8-9 years. It is easy to use. It is lightweight. It integrates out of the box with GIT, SVN, TFS and perforce (SCM softwares i've worked on). I think some SCM's also have it as a pre-built option in diff-tool setting. It compares folders as good as files. It has great highlighting of the line level differences. Easily catches the eye It also shows invisible characters in the diff as hexadecimal values. Worth the money for me.

I love how simple Beyond Compare is to use and how easily it displays results.