x10.com has recently taken to using popunder ads, which are even more insidious than popup ads.
However, there seems to be a way (as of this writing) to get rid of those ads, at least for 30 days, and if you're willing to accept a cookie from x10.com.
http://www.x10.com/home/optout.cgi?DAY=30&PAGE=http://www.x10.com/x10ads1.htm
However, it has been reported that you can disable the ads for even longer. Notice the DAY=30 in the above URL. You can change it to, say, 3000, so that the url reads as follows:
http://www.x10.com/home/optout.cgi?DAY=3000&PAGE=http://www.x10.com/x10ads1.htm
The above will (
theoretically) block X10.com ads for 3000 days. The
realist in me, however, doubts that x10.com will let it last that long.