WinMerge is an open source differencing and merging tool for Windows. WinMerge can compare both folders and files, presenting differences in a visual text format that is easy to understand and handle.
Diffinity is a diff and merging tool with focus on accurate and easy to read source code diffs. It will compare the content of two files and present the differences in an easy to read line by line and char by char basis.
P4Merge uses color coding to allow users to visualize the differences between file or images. It allows three-way merging among files, and shows side-by-side file/image comparison.
UltraCompare Professional is folder/file compare utility loaded with features to enable you to compare text files and folders, word documents, and even zip files and jar archives. UltraCompare includes text compare, binary file compare with the capability to merge differences...
WinDiff is a graphical file-comparison program published by Microsoft (from 1992), and is distributed with certain versions of Microsoft Visual Studio as well as in source-code form with the Platform SDK code samples.