Western Digital. Had 4 of those 40GBs, never had a problem. Had a 540MB, a 1.2GB, and a 8.1GB too.
Right now I have a 120GB/8MB cache and love it. I also have 60GB/120GB Maxtors, and hate 'em. Slow. Loud. HOT, too. Had to stick a fan blowing air directly over the drives to keep then from overheating.
A friend had a 20GB Maxtor in a full tower case, with a single case fan (it ran a 1GHz Thunderbird and a PCI graphics card, so nothing too extreme in the heat gen deptartment). You couldn't keep your hand on the side of the case next to the drive; too hot (when it was under heavy use, anyway). Yes, poor case airflow was a problem. Swapped the drive for one my old 40GB WD's, the problem went away. He did, finally, install another fan a week or so later.
Note that my 60GB & 120GB don't run as hot as the old 20GB did; but they're still way over the temp my WD runs at (less so for the 120GB, though).
That said, they are supposed to have the thermal problems under control now. Besides, CompUSA has a 250GB Maxtor for $133, no messing with mail-in rebates. Can't beat that.