I'm looking to buy an external portable HD for my 12inch PowerBook. However, after researching for a bit, it seems that some of them won't get power from the USB connection and requires and external power supply (which I do not want). So, I was thinking of going firewire, but then I worry not all computers have firewire or what if it gets discontinued? Does anyone have any suggestions on reliable portable HDs that work with the powerbook? Thanks.