Photographs and graphics that are licensed under Creative Commons or are in the Public Domain.
Flickr: The Commons - Photos from participating institutions such as NASA and The British Library. Search by keyword.
Morguefile - Free high resolution stock photos for creatives.They allow you to "copy, distribute, transmit the work and to adapt the work. Attribution is not required. You are prohibited from using this work in a stand alone manner."
Finding Free-to-use Images: List of several resources to find images, historic photographs.
Iconfinder - Miscellaneous icons sorted by theme.
Light Painting Photography - Tutorials, tools, tricks.