Most modern 2.5" IDE HDs should work. Make sure you plug the cable in correctly, as plugging a 44pin cable in backwards will fry the drive and/or the controller. I toasted a buffered IDE interface and a 8GB HD that way.
In my A600 I have a IBM Travelstar 2GB. But, before that I had a Connor 40MB and I've tested a Fujitsu 1GB. Never had a problem with any of them.
