web design help - need photos

I have a client that will require me to have at least 20-30 page header type images/photos, probably on a rotating basis. I suspect they will also want to change the photos from time to time. So, I need to have some business photos, construction, manufacturing, legal, etc. and a fair amount of them.

Can anybody recommend a resource to find and legally download such photos? Free would be great, paying for a collection would be fine, or paying on a per photo basis would be fine as well.

Thanks,

GL

sxc.hu

www.dreamstime.com

www.photos.com

www.istockphoto.com (this one more than the others)

We also commonly used is www.gettyimages.com but I believe it to be more expensive

Thanks fellas, found exactly what I was looking for.