A couple of products on RPGnow. (This info off the top of my head)
V Shane has put out some amazing art that can be used in your projects. But look for the Arcane "Publisher Editions"--they cost a bit more, but you have the rights to use them in print/PDF. And the quality of the artwork is exceptional. Most of the artwork is of equipment or items, but there are a few characters.
The normal Arcane series cannot be used in your products.
Another publisher has produced Image Portfolios that contain more of an "action scene". The quality of these is significantly less, and because it is more scenic, you may not be able to integrate the images into your product as easily.
There is/was a Stephen (Cook?) fantasy clipart collection which could be used for print products. Quality of the artwork was not a realistic representation, but had an interesting appeal to me anyway.
Of everything I've seen on RPGnow, my recommendation is for the Arcane Publisher Editions. The others are inexpensive enough that you may want to pick them up anyway, but don't expect as much from them.