Currently, and for the last few years, I've trusted Seagate hard disks. They haven't let me down yet.
(In my experience) The drives I've seen fail the most are Western Digital. Next are Maxtor, then IBM. I've seen one Seagate HD fail, and two I've heard of recently failing, a friend of mine's PC, but then his PC was a total bar heater, and I think that hard disks are far better off being kept as cool as possible.