Best Royalty Free Photo Sources?

The threads that were already here are old and I am sure this topic is evolving.

I know many of the common sources like sxc, 123rf, istockphoto, etc.

What I am trying to find are places to get photos that will be used to create videos which are then sold to small businesses. Another market is the creation of websites using photos in headers, etc.

If I understand the licencing on the common sites, the photos are one use only under those circumstances, meaning that I have to purchase a new copy for each project. At that rate I would have trouble competing against what I see as my main competitors. One of them claim they have a source like the one I seek that they have been using for 7 years. They, of course, will not reveal the source to me!!! (I believe their story)

thank you

Richard