You can do this from Kindle.. Go to Kindle Store and then to Owner's Lending Library. There are categories and subcategories and books are sorted by bestselling
I think it's a great question. I have an older generation Kindle 2, so do about half of my kindle shopping via a computer. It's too slow otherwise. (More specifically, browsing via a computer, specific purchases sometimes through the kindle.) I'd love to be able to filter to the lending library through my desktop.
If I have to browse lending title over 3G, I'm less likely to do it. Maybe that's the point.