For anyone struggling to find (cheap or free) stock.
Also, PhotoLibrary has full res watermarked images for download and the watermark is (usually) easy enough to brush out.
I've also found that using another search engine, rather than google, can get different results. Try altavista, yahoo, dogpile, msn or any other reputable engine for your image searches. They all use slightly different meta search algorithms, yielding different results.
Flickr ain't bad either.
Please add to the list if you have other useful sites!