I haven't looked for any free ones. I use www.istockphoto.com which does have a fee but it's not expensive. I just top up my account every 3-4 months when needed but I guess it depends on how many images you think you're going to need? Don't forget there are heaps with the Microsoft products which you can use if you're not onselling the items you use them for, such as a book.
I also use istock for my images, they have some very nice ones. But the problem of using these sites for images, is finding one to suite and also are not on many other VA sites.
I am in the process of looking for new ones for my site which I am upgrading at the moment. Hope to have it up and running again by the end of the week.
I like the "stock exchange" http://www.sxc.hu/ Some of the images are royalty free and there are some that you can purchase. I've used this site for years and love it.
If you require free stock images, try http://www.morguefile.com. Despite the rather unattractive name, it has a good selection of photos in many categories. The photos are taken by aspiring photographers and hobbyists so perhaps are not as stunning as those mentioned in previous posts but nonetheless, there are still many exceptional ones.
Free images for use on website?
Kels 
Linear Mode
