hardwood floors and spikes

Pennies work well. After time they do require replacement. The first time around I chamfered the pennies with a drill but now I just set the spikes in the center of the Lincoln Memorial. For extra thickness spring for nickels.

I have found the brass Audio Points and Coupling Disks sound great and protect my wooden floor.
http://www.audiopoints.com/

Linn "Skeets"

I use Nordost power points in titanium.
Not cheap but quite effective and virtually invisible

I just read one members suggestion about using pennies. I did the same thing but I had Hales Concept 3's (180 lbs) with three sharp cones each. They poked right through the pennies and left little impression of Abraham Lincoln on the wood floor. Pennies or nickels are fine for lighter speakers but try the brass coupling discs with felt on the bottom. If the speaker isn't too heavy you can even slide them on the floor without damage.