I found WinMerge Very helpful, WinMerge is an Open Source visual text file differencing and merging tool for Win32 platforms. It is highly useful for deeming what has changed between project versions, and then merging changes between versions.

• Visual differencing and merging of text files
• Flexible editor with syntax highlighting, line numbers and word-wrap
• Handles DOS, UNIX and MAC text file formats
• Unicode support
• Difference pane shows current difference in two vertical panes
• Location pane shows map of files compared
• Highlights differences inside the lines
• File filters in directory pane
• Moved lines detection in file compare pane
• Shell Integration
• Rudimentary Visual SourceSafe and Rational Clear Case integration
• Archive file support using 7-zip
• Plugin support
• Localizable interface via resource DLL