Xee

Xee is a free image browser that is used as a Preview replacement for MacOSX. It actually is very fast and uses little memory compared to other image browsing tools and uses OpenGL to help with processing the images. It’s very lightweight, but not a total replacement for Preview since it doesn’t do document processing.
Definitely useful if you’re looking for something to do what Preview does without the overhead for images.
Lifehacker < Xee