I have been very happy using the Stack Audio AUVA 70 isolators on my speakers. Tighter bass, better imaging, and increased clarity have been especially impressive. The larger AUVA 100 is supposed to be even more effective although it is also more expensive.
The advantage of the AUVA footers is that they are designed to provide stability for the speaker (so they don't tilt or bounce around) while also using dampening particles inside the footers that can prevent vibration from traveling from the speaker to the floor and from the floor to the speaker. Stack also has an excellent 60-day return policy that makes a trial with the AUVAs a low-risk investment.