Been experimenting with floor debris the last couple of days and it seems that 5 sided small rocks seem to produce the best results for variety. I initially created a set of 6 different shapes, then a couple of small groups (different shapes, sizes, orientations) and finally sprinkled the groups around the blend edges not the cave walls. Saving the cave wall edge for larger rocks works better. I also used a lower phong value (60) and it really does bring out the cave wall edges better.
http://www.simonoc.com/images/design/maps_q3/moteof1eq1.jpg
@necros, I have D3 installed if you want some help testing stuff, but I won't be able to help till after Jan 12th. Got a city trip planned for next week.