When I moved into my house last year, I bought an LG front-load washing machine. Having never owned or operated a front-load washer, I didn't quite know what to expect. For those who don't already know, front-load washing machines typically spin clothes at a very high rate of speed (mine tops out at 1050 RPM), removing a large amount of excess water in the process. This high speed spin process usually results in substantial vibration. The problem is compounded when the washer is located in an upstairs room (as mine is), and not on a solid, ground level floor (I've read that concrete floors are ideal).
Not knowing about this at the time, I was really surprised to see that my entire house vibrated when I washed a load of laundry. The shaking and noise got bad enough that I decided to look into solutions to the problem. I read some about vibration reducing pads online, and picked up a set at a local home improvement store (for about $30, if I remember correctly). After installing the pads with the help of my dad, I noted an improvement in the amount of vibration in the floor. However, the vibration was still bad enough to cause some sympathetic vibrations in my dryer (a major source of noise, oddly enough). Also, these pads were flat on top, so the washer tended to 'walk' off of them when a load was particularly unbalanced. Like before, the problem became bad enough to look for another solution.
I found another pair of pads online that had good reviews, and picked up a set (here's a link: Good Vibrations Washing Machine Pads). These pads are round, not square like the others I had bought, and have a recessed area for the foot of the washing machine.
Wow! Not only does the washer no longer walk off of the pads (thanks to that recessed area), but the vibration in the floor has been reduced by what seems like an order of magnitude! My dryer no longer suffers from "sympathetic-vibration-syndrome," and the entire wash cycle is noticeably quieter. A set of four pads are $36.95 as of this writing (plus shipping). The sellers accept PayPal, so if you've got some money stored up (like I did, thanks to a recent donation to Born Geek), you can pick up a set pretty easily.
If you've got a front-load washer and have issues with large vibrations, I recommend the "Good Vibrations" pads. They work remarkably well.