power mac g-5
If I want to replace my Power Mac G-5 with a new product, which one would be comparable?
PowerMac
That's kind of hard to say except another G5. If you want a desktop like a flexible, upgradeable box then a Mac Pro. Anything, even a mini, is likely to be faster. Macs are really developing more along the "smaller" side of things so notebooks are more popular.
You really need to tell us what it is you do with a computer.