I used to use what we in the U.K. call Blu-tack, a pliable putty material similar to plasticine, between the speaker base & the stand. But since discovering Herbie's range of wonderful products, I've used their Big Fat Dots which improves on Blu-tack.
In addition to the speaker/stand interface, I have just discovered the importance of the interface between stand & the floor. I used to just use spikes onto a base metal disc on my hard wooden floor. I just received a set of Herbie's Cone/Spike Decoupling Gliders, which I tried on both my main system's Von Schweikert VR4jr speakers & my old stand mounted Linn Sara speakers of my home cinema system. I was expecting these Cone/Spike Decoupling Gliders to just improve the bass on my VR4jrs, which in my room, can sound a bit boomy on certain CDs. Well, it improved the bass alright, but more than that, these Gliders brought an big allround improvement to detail & sound-stage. The improvements are not subtle, but is unmistakable and clear on first listening. For the very reasonable price that Herbie's charge for these ($12.50 for one), its a no-brainer in my view.