http://www.adigitaldreamer.com/gallery/
I found this through DIGG, so some of you may have already seen it. It's a small but excellent collection of free, royalty-free, stock photos. There are some very nice landscape photos and at least one tree I expect to show up, here, in someone's artwork.
While there, check out the rest of the site for a few Photoshop brushes and some Fonts.