Anti-Vibration mats for top loading washer?
Yes they work.  They distribute weight across a wider area and also act as shocks.  

However the most important thing is to make sure that your legs are firmly on the ground and the weight of the wash machine is evenly distributed across all 4 legs.  If you don't do this then the mats become useless.  

Also since this is a DIY site I will point out what I use on my washer.


Buy cheap plastic party cups.
Buy silicone caulk.
Cut party cups so that they are only 1.5" tall.
Fill to at least a .5" (up to .75") - all cups should be filled equally.
Let silicone cure (could take a few days).
Balance wash machine.
Sit cups under.
Notice that cups make a scratchy sound so put felt pad under them (this could be step 6).