If you just want a better power cable then I'd recommend
THIS one from Mark Grant. Actually I'd recommend any of his cables. They're all great quality and fantastic value.
As for mains conditioners, I currently use a Tacima which I found ok but not much of an improvement. It actually made my amp sligtly worse in some areas. One thing you need to understand about low end mains conditioner blocks is that while they do clean up the power they actually rob some of the dynamics from higher powered equipment like amps etc. So they work best on low power devices like CD players etc.
For higher end conditioners for use with power amps etc I'd check out
Isotek.