Meld is a GNOME 2 visual diff and merge tool. It integrates especially well
with CVS. The diff viewer lets you edit files in place (diffs update
dynamically), and a middle column shows detailed changes and allows merges. 
The margins show location of changes for easy navigation, and it also
features a tabbed interface that allows you to open many diffs at once.

WWW: http://meldmerge.org/