Each day, this site features a different image of an astronomical object, accompanied by a descriptive explanation written by a professional astronomer.
Captions have links to further information on topics related to the image.
The Solar Data Analysis Center at NASA Goddard Space Flight Center has a stellar image archive. The most recent, full-resolution solar image of each type is in the SDAC archive. An archive of many astronomy images. A large site consisting of many catagories. The AAO has made available a collection of spectacular color pictures created by David Malin.