ACDSee - ACDSee is an image viewer that uses very little system resources, and it has a small, sleek size that won't take up much space on your system.
PixBuilder - Free Photo Editing Software for PC
digiKam - Professional Photo Management with the Power of Open Source
PhotoDemon - Lightweight portable BSD licensed photo editor for Windows focused on performance and usability.
Flickr - image and video hosting website
Fotografix - In addition to being totally portable, Fotografix has a ridiculously small footprint.