Open Clip Art
Try Open Clip Art for all your clip art needs. It has whole wealth of Clip Art organized in tags and most of these images are in Public Domain which allows you to reuse them anywhere you want. You can even download the entire Open Clip Art collection to your hard disk in svg and png formats. See how you can integrate Open Clip Art with Open Office or use it with Microsoft Office Applications. Some files at Open Clip Art may not be available in png format you can still download the SVG file and convert it using free and open source tools such as Inkscape or the Gimp. You can also use these images on Google Docs and Google Sites too. But please do not link directly to the image file on Open Clip Art’s server. Instead download the png file to your hard disk and then upload it to your document.
Flickr
Try Flickr’s Advanced Search to look for images, pictures, photographs, drawings and other art work that are released under a creative commons license that allows you to redistribute or build your work upon them. This license is called Creative Commons Attribute. You will be surprised to see how much high quality content is available for you to re-use.
Remember using someone else’s work without their permission is not just bad manners but it is also copyright infringement. Most people on the web do not mind sharing their work, after all thats why they publish it on the web in the first place. Instead of stealing someone’s work it would be much better if you ask them politely to use their work on your website or document. Don’t forget to mention that you will give them the credit for the work.