Spikes and hardwood floors.....what to do?

Adona Corp's discs worked for me. I got the bigger one's, still really cheap. A penny might leave an imprint in the floor, especially if you have alot of polyurethane coating.

home depot pads...2 to 3 bucks

You could also determine the optimal location for the speakers with the spikes removed, and then replace the spikes and carefully set them in place. As long as you never move (or bump) them, the worst you would have is some small pin holes that probably wouldn't be noticeable.

Slip and stick feet from HD or most any home center these help damp vibrations but also stick to floor without damage once you break this friction seal you can easly slide loudspeakers over floor again without damaging.Once they sit a few mins they stick again wonderful feet I use these on my loudspeakers.Much better than cones or spikes.Work on carpet but if speakers tippy than you might still want spikes on carpets.

Pennies and other small change have always wound up being pierced by the spikes when I've used them.

A brass or stainless steel disc made for the purpose is a better bet and there are lots around. For vibration decoupling and an improved upper midrange, try a Herbie's dot under the disc.

(Steve Herbelin actually sells metal discs with damping pads attached, he calls them Herbie's Grounding Bases, but they cost more than some other devices.)

http://herbiesaudiolab.home.att.net/footers.htm