Another recommendation for PS Audio power regenerators (and a vote against UPS distortion-makers and expensive power filters that end up reducing the power to your components). I went from the P300 (great, but I needed more power) to a P500 (even better, but then I got a nice speaker amp that needed even more) to a Premier (finally, a power product that not only handles my 250W speaker amp, but actually makes it sound better).
I've auditioned Balanced Power Technologies (OK I guess...actually, it really didn't seem to do anything), Shunyata (nice I guess, except for the power reduction resulting in insufficient bass), and an APC UPS thing that I used to use with my computer (yuck).
If you are looking for something simpler (and less expensive), the only filter I've used that didn't make my setup sound worse is the new PS Audio Duet (warning...the older PS Audio filters, like the Ultimate Outlet and UPC-200, are not nearly as good).