File Merging/Comparison Tools

Eclipse provides file merging out of the box. Even though no additional plugins are required to use file merging, I personally don't prefer to open eclipse just for file comparison.

Windows tool
WinMerge is a open source comparing, synchronizing and merging tool for windows.
Features: 

• Visual differencing and merging of text files
• Flexible editor with syntax highlighting, line numbers and word-wrap
• Moved lines detection
• Folder comparision including sub folders
• Works like a version control, creates patch files, resolve conflicts

Notepad++ plugin

 The simplest way to compare files is using npp compare plugin. After installation of this plugin, we can enable file comparison with a shortcut and it compares last two files opened in the notepad++ windows.