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Unfortunately there is no definitives answer as apple uses drives from multiple manufactures:So far I've seen, toshiba, hitachi, and seagates used in macbooks.
 
my macbook came with a 5400 RPM 80 GB Seagate. I upgraded it to a 120 GB Seagate. You can never go wrong with a Seagate.
 
Barefeats has some good rundowns of different size/speed hard drives in Apple notebooks. As mentioned before, though, Apple uses many manufacturers, so you never know what you're gonna get.
 
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