Diff Doc - Compare files with 'Diff Doc' by Softinterface. Compare DOC DOCX PDF TXT RTF HTM XLS PPT. Command line capable for automating comparison of files.
AptDiff - AptDiff is a visual text / binary files comparison and merging utility for Windows.
WinMerge - WinMerge is an open source differencing and merging tool for Windows.
WinDiff - Download Windiff : free files and folders comparison tool
Tkdiff - tkdiff is a graphical diff viewer based on the Tk framework.
Online Text Compare - Online Text Compare tool allows you to compare two documents in different formats.