I've been doing the same exploring glad you brought it up. I like slide shows too.
Fluid is terrific.
Graphic Converter can do very nice random slide shows with some QT effects, tiling etc. Really does a nice job on travel photos etc with lots of control. I have it running on the second monitor for eye candy while i work.
Seti of course is useful - a bit boring but hey you never know
iViewmedia Pro does a nice job on slides AND it can run in the background so with it's tiling it changes the images in a controlled manner.
The cutest is Exhibition X which has very neat OpenGL effects bringing your slides and images in different views - the Cube one is very neat. It can also operate in a resizeable window so you can keep images rolling while you work.
Having fluid overlay one of these is but it works the machine and your video card hard.
I'm grazing the edges of the G5 smooth and quick zone as I've got twin 21" monitors each with multiple images
Of couse Mac Aquarium is terrific, the new clock version is very cool.
Here's a cool utility that will turn your screen saver into the desktop on your powermac. You need a pretty powerful graphics card for this to work. I have been using it on my G4 733 and dual 867 MDD and now my G5 1.6