Im of the opinion that the new iMac will fill the bill pretty well. For a long time I was a major proponent of PowerMacs for my own personal use, feeling that I NEEDED the extra power and expansion capabilities. But in the past few years. I've found that my own perfect setup is actually an iMac/iBook combo for the price of a PowerMac. I've been doing digital design for about two years now and, for the most part, my 1GHz iMac G4 and 800MHz iBook G3 have done me well. There are times when they could be a bit faster, but for 95% of the time they're perfect.
But if you're dead serious about pursuing either 3D animation or Video Editing, maybe a DP PowerMac would be a better choice for you. You'll want all the processing power you can get for 3D, and I imagine those PCI slots would come in handy for DV Editing.