iStockPhoto is a stock photo library where royalty free images can be downloaded for US$0.50 to US$1.50. The images are uploaded by amateur (and professional) photographers who get one fifth of the download fee as a royalty (i.e. 10-30 cents). Once you have earned $100 they will send you a cheque.
So far I have accrued the princely some of US$2.00, but it is still cool to see people actually paying money for your photographs.
You can check out my portfolio here.