Actually, just goofing around, I installed a Hitachi 500GB hard drive in my new generation MBP 15" last night. I was in Fry's Electronics over the weekend, and they had the Simpletech Signature series 500GB USB hard drive on sale for $119. Picked it up, and thinking about it once I got home, I cracked it open, curious to see what drive was in it. It was a Hitachi drive, exactly the same as the Hitachi drive that comes in the new MBP 15" (except for the 500GB of storage, of course). I replaced my 250GB with it, popped in the Leopard install disc, restored from a Time Machine backup, now I'm rocking along with double the storage of the standard MBP for not much more than Apple wants for the 320GB in the MBP.
Here is a link to the Simpletech drive I'm talking about.
http://shop1.frys.com/product/5700662?site=sr:SEARCH:MAIN_RSLT_PG