I find Fotolia are the best picture library for royalty free stock images.
A friend put me onto them when I was looking for cheap royalty free stock images and they've always got what I'm looking for. They're fairly new to the market, but growing rapidly so they are adding new photos all the time.
For web design I usually only spend 57p/$1 per image (72dpi). But if I want to use it as a print image than I will buy the 300dpi one at just double that.
I also like the way they have another licence you can buy which allows you to print the images onto posters or canvas and resell them like that. I think they call it their Extended Licence (?!). Costs a little bit more, but not many royalty free stock images allow you to do that - and I find you never know what surprise a client will want to spring on you next!
Not sure where you are, but they've got a few sites as they are worldwide - all the same images but they've got French/German and Spanish sites as well as English
Try:
http://www.fotolia.co.uk
http://www.fotolia.com
They've also got some free images available for download, but to be honest, I'd rather play the game and cough up for good pictures. At these prices even I can afford to.
Good luck with that!
D-Sign/Angie