PatchEditor

Start the client here if you have Java 1.5 installed

PatchEditor is a A simple easy-to-use application for "visually editing" of large patch files (diff files); different patches/diffs/folders/files can be selected/deselected, the resulting patch file can be saved and/or run against a source tree (e.g.).

Features:

Simple and un-bloated
Efficient (hotkeys, no mouse navigation needed etc)
User-friendly, tool tips, etc
Multiple tabs / patchfiles
List of MRUs (Most recently used files)
Saves last used directory etc
Localization support (currently 3 languages supported)
Developer friendly distribution; build scripts and Netbeans 4 project information included

Requirements:

Java 1.5 or later

But of course, we all know you're here for the screenshots. Here is the best we have:

Screenshot of PatchEditor after opening a patch file and adding some patches to the output