Pierce Audio, makers of the MOAB, WMD, WMD2, and OEMs of the first gen. Cascade Omegas I believe, as well as many many other speakers over time I'm sure. These are just the ones that come to mind.
I have a 15" Nightshade D2 that I have ran since the end of February for sale. Ran it in 3.16 cu ft at 36 hz off a 3000d and it sounded perfect. Did a 145.9 at 38hz but my truck is quiet. PM me if interested.