I've said this before and I'll say it again: you should NOT use google images to find stocks. You don't know what you're taking, and it could get you into some serious trouble. It doesn't matter if it's just a signature or LP for some random contest, good practices should start early, and if you were to give a paying client a design that included a stock ripped from google images, you could potentially be playing with fire.
As far as stocks goes, if you've got money to spare, use it.
www.istockphoto.com
www.stockxpert.com
www.corbis.com
www.fotosearch.com