I have a matched pair of DDR4000/PC3200 256MB sticks that just came out of my G5. They are guaranteed in working order - I took them out to put a 2GB kit in their place, and my G5 was quite reliable with them in. If I am not mistaken they're the original 256MB modules that came from the factory with my G5. They are labeled Nanya NT256D64S88B1G-5T, 256MB DDR-400MHZ-CL3, PC3200U-30330. I know they're only 256 so they may not be useful to anyone given how amazingly cheap higher capacity modules are now and how old the compatible (AGP-based) G5 line that takes them is, but I have no use for them at this point.
$30 shipped, other offers considered.