Walker Audio makes brass discs, filled with lead that not only protect the floor, they often sound better. And, Sound Anchor makes hard "chrome" discs, with a kevlar pad on the bottom, it's as soft as a rug, and yet highly resistant to compression. The suggestion about the pennies is correct too. You could begin with them, and continue the experiment, if need, after you become accustomed to your new room.
Alternatives to speaker spikes?
I have a pair of Paradigm Reference 100's with spikes at the bottom. I'm moving into a newly built apartment with beautiful hardwood floors. What can I do to prevent ruining the floor?