Tyll - some of us really love the MDR-SA5000. I've seen conflicting reports over whether Sony still manufactures it, but I think it deserves more listeners here. It deserves to be recommended along with the HD-650, K-701 and DT880.
Please also consider the MDR-7509HD. I'm one of the few people here who own one and I've been impressed with it. It deserves more attention and more representation here.
You should definitely carry the venerable MDR-V6. Along with the SR-60i, it is one of the very best entries to good headphones. If you can swing a good price on the V6, a lot of newbies will give them a try.
While they aren't Sonys, how about asking Beyerdynamic for the DT48? They're developing a following here and I'd love to see your measurements for them. I think the only other US distributor is B&H, so it would be nice to see HeadRoom pick them up, too.