AptDiff is a free visual text/binary files comparison and merging utility for Windows 2000, XP, 2003 and Vista that features a double-pane view for side-by-side comparisons, with customizable color-coding indicating whether each line/byte is added, deleted, or changed.

Key features of AptDiff include:

-Compare Files directly from Windows Explorer.
-Easy navigation through the differences.
-Automatically detects file changes: Watches for changes when file is loaded in AptDiff and reloads it if required.
-Customizable keyboard shortcuts.
-Command Line Support.
Automatically move to the first difference when loading.
-Merge all/differences for text comparison.
-Generates comparison reports in HTML
-Unlimited undo and redo
-Binary files comparison(byte-by-byte).
-Navigation by differences within bytes.

Download AptDiff for Windows here