PhotoShelter has done an important survey of buyer attitudes and preferences when it comes to your website. They have very kindly offered to share the results with everyone. You can get them here (yes, you have to enter your email address, but it is worth whatever marketing they may do).
One small think to keep in mind as you read the report is that PhotoShelter asked buyers who were generally more stock buyers than assignment buyers. Overall, I think their data matches up very much with what I have learned in my own surveys of assignment buyers, but the two notable exceptions are that a page full of thumbnails is not very well liked for assignment buyers, and you shouldn’t (generally) put your assignment prices on your site.