How to stabilize speakers without spikes.

I would try Cerapucs by Finite Elemente. They do not have spikes to damage the floor and come in several sizes. See info:
http://www.musicdirect.com/products/detail.asp?sku=AFINCERAPUC

type in adona in the audiogon search and scroll down to his floor spikes and protectors for some ideas.

If you don't have a carpet anymore, there is no reason to have spikes since there is nothing for them to bite into and improve stability. Just use the brass discs alone or coins. Hockey pucks might be a better solution for a wood floor like someone else suggested.

Depending on what's under your hardwood floors, spikeless speakers might work well.

I recently sold my ProAc Response 2.5s to a co-worker who after almost 2 decades of being off the merry-go-round has begun building a system again. He had no idea how to install the ProAc plynths and spikes so he just placed the cabinets on his hardwood floors. When I went over to have a listen and help him tweak the placement I was shocked at how stable the speakers were and how great the bass sounded. It turns out he had concrete under the hardwood and the floors were well leveled.

I brought over some brass cups for his speaker spikes, but it turned out they weren't necessary.

you can still use spikes but you will need to get either the support discs or Target Spike Shoes. Support discs from Music Girect are all metal, they are affordable and do exactly what they supposed to besides there is no sound degradation. Target Spike Shoes that Cable Company sells are also affordable. They are metal on top but rubber on the bottom. I have spike shoes under my SolidSteel 5.4 component rack and Support Discs under my speakers. And use spikes without any damage to the floor.