There was a time when web developers and others would have to pay incredible amounts of money for stock photography.  I remember having to pay $30+ for low-res images, and a lot more if you wanted to put a high res image in an ad.  You could always go to Google images and take what you find, but you could run into some copyright issues.  Here are a few site you can use to save a few bucks on images, and reduce your risk of being arrested:

Free Images:

Nearly Free Images:
• Big Stock Photo