Western Digital 120 GB w/8MB buffer. Mine works like a charm. I have it, along with the 80 GB Maxtor that came with my HP. I'm thinking of getting the new WD 200 GB HD, switching it out with the Maxtor, and then I'll have 320 GB internal. I can then put the Maxtor in a FW enclosure externally.
Get anything recent, they're all plenty fast. The Sweet Spot seems to be 120GB.
As an aside, I was watching the "www.techbargains.com" site last month, and Dell had a super blowout kind of deal on the WD 120GB 7200. After discounts and rebates, net price came to $56! Free shipping to boot.