I use the Wilton Crystal-Clear Cake divider set plates. They are also the plates used on the Wilton Floating Tier Cake Stand. Then I use the Wilton Hidden pillars. They work Great, no I don't have stock in Wilton!!
I just found where I ordered them-www.bakingshop.com
They are not true hidden pillars, but can be cut to size and used a hidden pillars. it doesn't say they can, but I took a good look at the wilton, and it appears that they are just trimmable columns. You just trim them slightly above the cake so it will look as though the tiers are floating.