I am a great fan of Stillpoints and use the origonal units and now the Ultras under my turntable. There is another excellent choice to consider, at a comparibly high price, I am afraid and that is Track audio isolation feet. I have used them under my Daedalus speakers for about 2 years, after trying spikes, granite blocks, Finite Element Cerapucs etc. They made a very significant difference, tighter and deeper base a generally crisper, more detailed sound.
I have not compared them with the Ultras, but would recommend trying them, if you can get ho;ld of demo sets, they are available in the US
www.trackaudio.co.uk