I don't know of its availability in the US, but Tacima and Lindy make a highly respected mains conditioner/mains extension for about £30. Just don't plug amps into it as that saps the dynamics, unless they are low powered ones such as headphone amps. You can tell how effective they are by listening to background hiss before and after use. The hiss should be reduced. If it is not, then it is likely your mains are quiet and you do not need one. Try it at different times of the day as the voltage drops in the evenings as more people use other electrical items and rises again later at night as people go to bed. That also affects the noise in the mains IME.
As for cables, I would not bother as testing, of which we are not allowed to talk about here, has found no one can actually hear a difference between them.
Edited by Prog Rock Man - 10/28/10 at 4:15am