Oh yeah, I forgot about the Symposium inserts! Users have reported good results. Owners of the Seque platform have also reported excellent results with unsuspended tables, and a set of Roller Blocks (or similar roller bearings) between the table and the Seque may provide even more isolation.
Another option is the Townshend Seismic Platform, or the Seismic Pods under a shelf of your own choosing. Either way, very effective isolation at relatively reasonable prices. To do better, you have to go to the microscope isolation platforms, at around $2500 and up. Ouch!