As far as the Power Mac goes, I hope Apple offers the GeForce 7800 series sooner rather than later. The Power Mac should always offer the best current video cards as an option.
The PowerBook's Radeon 9700 isn't bad even today, but I imagine it will be replaced with a Mobility X800-series card - but not until the switch to Intel takes place. Maybe the 128MB version will become standard on last G4 PBs. The base config will probably be a cheaper Radeon, like an X600-class.
One more niggle: It would really be nice if Apple offered Pro cards for the G5 such as the FireGL or Quadro. They've never been available, and would improve Apple's benchmarks when comparing various professional software packages across platforms.
The Nvidia GeForce/Go5200 wasn't a bad card in it's day, but its day has clearly passed. However, as a "base" configuration card it is still OK - it has plenty of power for the average user, and performs decently with games like Halo and Call of Duty. It will be around for a while yet - my guess is that it may make it's way to the mac mini at some point, unless the Radeon 9550 gets there first.