What's under your bookshelf speakers?

I recently picked up a pair of ProAc Tablette Reference 8 Signatures in bird's eye maple for my office system. I would like to protect the finish on the bottom, but also preserve/enhance the sonics. At the same time, seeing as how this is in my office, I would like to keep things visually discrete. Currently, I have a small mouse pad underneath each one, and in truth, this seems like it might be a viable option. However, I haven't tried them with another product underneath them or with nothing underneath (don't want to damage the finish), so I am not sure what sonic effects the mouse pads are having. The system sounds pretty good as is, though.

Thanks, Tom.
Thanks for the heads up. Damaging the finish is the last thing that I want to do. In truth, the mouse pads don't look too bad. They are only slightly larger than the speakers, and I could always trim them down to size.

I use the stuff that is used to keep area rugs from sliding around. It's available in various sizes at home centers or discount stores. It's only 1/16" thick and can be cut easily with scissors.
A very similar product to what Mijknarf suggests is a rubberized shelf/drawer liner that you can buy anywhere - Walmart for instance. Comes in a few different colors (not that you'll see it under the speakers) and in much smaller sizes than the product for area rugs.
I'm glad I asked this question! These are some very innovative ideas!

Thanks, Tom.
stick-on rubber feet from the hardware store.