Re: power conditioners
The cheaper ones aren't that much different from a good power strip with protection and RF filter. You might want to check your hardwarestore first if you're planning on going for the most "wallet-friendly" option.
Mr. Venom is bang on about the Voltage regulator, it gives your tube amp the exact steady voltage it needs, regardless what comes out of the outlet. This is particulary handy when you're playing at an open air festival and you have to rely on a dieselgenerator or some other thing that won't give you a steady thing to begin with.
Should I live long enough to see the day when the bits to go in my amp are finally shipped, I'm going to get me a rack with a powerconditioner first though. Any protection is better than none and the PC should help me while I save for a VR.
Besides, I also want a noisegate in the rack, a tuner, a drawer for a couple of pedals and quality wires to hook it all up.