IMO, it's best to buy the external enclosure and drive separately. That's about the
only way to be sure you're getting a high-performance drive -- and it's often less
expensive than a "pre-assembled" external with an "economy" drive mechanism.
With a separate external enclosure it's easy to upgrade or swap drives (without
voiding the warranty) -- you also get the drive manufacturer's full warranty
coverage (5 yrs for Seagate drives). ...just TRY to open a MyBook sometime!
There are lots of good SATA-based enclosures (look for an Oxford OXUF924/934
chipset). Here are my favorites -- good prices, handy slide-in trays, quiet (fanless),
and simple assembly (four screws, no messing with internal cables/connectors):
Icy Dock USB/FW800 enclosure @ $80
Icy Dock USB/FW400 enclosure @ $45
Icy Dock review & photos (USB/FW400 version)
Some FAST drive mechanisms: (> 100 MByte/sec sustained R/W)
500 GB: Seagate ST3500320AS, Samsung HD502IJ
750 GB: Seagate ST3750330AS, Samsung HD753LJ
1000GB: Seagate ST31000340AS or Samsung HD103UJ
Any FW800 external will work on a FW400 port (with a cheap 6-pin to 9-pin
firewire cable). So, more expensive "quad interface" drives have no advantage
over simple USB/FW800 units. (The eSATA interface is useless with iMacs.)
LK