If you're in a desperate need for high quality HDR images for a commercial work, I think it's worth a look at HDRI-locations.com.

This is run by the known artist Thomas Suurland, who offers some good free resources on his personal site. By the quality of his personal works, I believe his HDR maps may be on the same level.

I don't have any affiliation with him or his image-selling website. I just think that's cool to have an artist-driven resource for other artists who need to make commercial works.