Other
University of Leicester: Irregular Galaxies
Provides a general overview of irregular galaxies, including a specific look at type I and type II irregulars.
NASA
Nasa: Antennae Galaxies
This image, titled "Fire Within the Antennae Galaxies" features three individual pictures of the antennae galaxies taken with different equipment (x-ray, infrared, etc). The text under the image details various specifics about the picture.