Alternative for WinMerge in Ubuntu

"Meld (alternative link)
Meld is a visual diff and merge tool. You can compare two or three files and edit them in place (diffs update dynamically). You can compare two or three folders and launch file comparisons. You can browse and view a working copy from popular version control systems such such as CVS, Subversion, Bazaar-ng and Mercurial. Look at the screenshots page for more detailed features."

gvimdiff is handy for quick comparisons. Install gvim to get it.

"The open-source tool Kompare is worth adding to your diff tools on linux:

It makes effective use of color
It works great form the command line to pipe recursive multi-file diff sets directly from Subversion (or any other version control system)

[~/path/to/project/source]$svn diff | kompare -o -
Works great with Gnome Ubuntu even though it is a KDE native app.

To install on ubuntu: $sudo apt-get install kompare"