I see this topic quite often, so I thought I'd link to a product I just discovered that might help some of those who want to do this.
http://www.tricklestar.com/html/s01_home/home.asp
Note that the PC version uses USB to turn the outlet on and off. So I'm assuming that just supplying 5V to a USB plug from Arduino would work. (I don't know how much current would be needed.
They only cost about $17USD and they have 120v & 220v models with various plug types. The 120V version will switch 10A. Google for one in your neighborhood.
Note: I don't own one (yet) and don't work for them. Just wanted to pass this along in case it helps.