Here's two great sites that I use regularly for free, copyright-free/creative commons images:
- StockXchange: features some great quality stock photos by professional/semi-pro photographers. You need to sign up to use this site, and may occasionally need to ask permission from the author to use their photo. But for the scope and quality of what's on offer here, it's really worth it!
- Creative Commons search engine: I came across this excellent search engine through Blogger: you can use Google to search only images and video which are published under a creative commons licence. Loads of great photos and images available; authors are usually amateur/semi-pro, but there are some real gems to be found. And you don't need to sign up to use the site!