I used
Stock Exchange for free images all the time when I doing projects for school, but they don't have the greatest selection. You can find a lot of sites (search for "stock photography") that will sell royalty free images, most have an option to search for only "royalty free". You still have to pay for them, but at least you get unlimited usage afterwards. They can be found, but you'll be spending quite a few hours finding stuff you like.
I know I discovered a few of the images we used at my job were NOT royalty free, fortunately they weren't on any publications or packaging. You get yourself in a lot of trouble using images you didn't pay for, and it's just not right. Make sure your boss understands that.
http://www.istockphoto.com/ http://pro.corbis.com/ http://www.shutterstock.com/ http://www.firstlight.com/