I think the commercial grade Oneac and Powervar's are the best bang for the buck. These can be had on ebay for pennies on the dollar. They're actually designed to clean power for labs and other places where semiconductors that are sensitive to dirty AC are. I know some equipment manufacturers in the industrial world require one of these or they will not honor their warranty. They're not as pretty as the audiophile ones but do the job. That said I wouldn't use one with a power amplifier as they have isolation transformers in them. Actually if you bought a huge one you could use it for an amp. Even the small ones are pretty heavy though. You want to make sure you buy one that is at least twice as big as you need. For front end gear even a 5 amp one is more than enough.
