RAM will get you into trouble with the AmigaOne because there is a thin compatability list there... and I don't know of any AmigaOnes motherboards for sale in the US.
I got my MicroA1-C from Software Hut when they still had them but I don't think they have any more...
BTW my MicroA1C came as an installed and preconfigured system with a DVD-ROM reader/CD-ROM burner. I can verify it can read DVDs (although coming up with a player program will require MPlayer which is still in the testing stages) and burning CDs will require either FryingPan or BurnIt.
Also the newest configuration available is just a 1.4 GHz G4 card that costs a lot and is available for AmigaOne and MicroA1-C but not MicroA1-I which isn't released yet and will have an 800 MHz G3 soldered to the motherboard.
G5 is incompatible with the Articia S chip and so will not be available for quite some time. A likelier option for the future is that AmigaOS 4.1 may support multiprocessing making dual-core G4s a better and more cost-effective option.
