In my webinar handouts I include additional links that you might find useful, and apparently in my latest handout the link was corrupt. So rather than making you dig through my blog for where I posted that in the past, here it is again... http://bit.ly/CfG69
And one thing to consider...why would you want to pay for images?
I happily use istockphoto and a few others in lieu of searching for free images simply because of time.
One, 100 sites is a lot of sites.
Two, many have restrictions such as the 'free' image only being low resolution or a small one (and they may not look good when you expand them to fit an entire slide).
Three, the search engines for paid sites tend to be better, and this is the biggest reason for me. The reality is that finding just the right image can be time consuming, even with a good search engine. As a professional speaker and trainer, I figure it's worth it to me to pay for quality images that I can find much more quickly because of both the search engine and familiarity with the site (it's like knowing your favorite grocery store...you know where to go for what you want). But that's just me...I count it a cost of doing business.