I've used the Auralex SubDude and Great Gramma with good results under my Velodyne subwoofers.
Here is an older thread where other A'gon members have shared their thoughts on the Auralex SubDude. Seems to be the real deal.
SubDude
Here is an older thread where other A'gon members have shared their thoughts on the Auralex SubDude. Seems to be the real deal.
SubDude