PixBuilder - Free Photo Editing Software for PC
RealWorld Photos - RealWorld Photos is an free portable photo editor for Windows.
PhotoDemon - Lightweight portable BSD licensed photo editor for Windows focused on performance and usability.
Online Image Editor - Online editor for images and animated gifs with multiple effects and tools
Fotografix - In addition to being totally portable, Fotografix has a ridiculously small footprint.
SoftColor PhotoEQ - SoftColor PhotoEQ makes color correction, image editing and color management tasks simpler.