When designing websites, one of the hardest tasks can be finding images and other media that won't get you in trouble for copyright infringement. Here are some resources (man culled from a post at LifeHacker) for finding content that is in the public domain, reusable under Creative Commons licenses, or reusable under the GNU Free Documentation license:

Wikipedia's list of Public domain image resources. Public domain images

Creative Commons Search. Search content published under Creative Commons licenses

Wikimedia Commons. "Freely licensed photographs, diagrams, animations, music, spoken text, video clips, and media of all sorts."

ccMixter. Community music site featuring remixes licensed under Creative Commons

ccHits. Creative Commons-licensed MP3 index

LifeHacker's list of stock photos. Stock images

MorgueFile. Stock images.