My 2 cents: Once you get a new external HDD, sell that WD external. You'll be lucky to get 1 year out of it. I've had very bad luck with WD external drives. Maybe they don't like the heat in an external case, I dunno.
As a rule of thumb I would recommend any drive that has at least a 3 year warranty. If the manufacturer doesn't have enough faith to warranty it for more than 1 year, you shouldn't trust your data to it.
I like Seagate externals IF you're going to buy a retail external.
I would suggest, however, building your own (buy an enclosure and a drive separately - and buy a Seagate drive with a 5 year warranty). Why? Most of the retail externals are deliberately made hard to disassemble. It's almost impossible to open most of them without busting the case.
There are times when you may want to or need to remove the drive. For instance, you get some data corruption and you want to run Spinrite on the drive. Spinrite will work on a USB drive BUT it will not do as good a job because it can't access the drive subsystems directly. It defaults to a "virtualized" mode when working on USB drives which is less than ideal (it's also SLOW since DOS can't access a drive at more than USB 1.1 speeds). Steve Gibson himself recommends taking the drive out of the enclosure and directly connecting it to the PC to run Spinrite on it properly. Same applies for most low-level drive utilities. USB drives always run in a hardware abstraction mode that doesn't give full access to the low level functions.
So this is what I'd recommend:
VANTEC NST-360SU-BK 3.5" eSATA + USB2.0 Aluminum External Enclosure - Retail $33.99 (I have 3 of these and they are excellent enclosures):
http://www.newegg.com/Product/Product.a ... 6817145167
Seagate 1Tb 7200RPM HDD $129 (5 yr warranty):
http://www.newegg.com/Product/Product.a ... 6822148274
Seagate also has a 1.5Tb drive for $229, but frankly I think it's too pricey and I never like buying a new HDD technology. The 1.5Tb drives just came out and they need some time to work out the bugs. The 1Tb drives are rock solid. I'd rather buy 2 1Tb drives than the 1.5tb drive. If you're interested here's the link:
http://www.newegg.com/Product/Product.a ... 6822148278
ALSO do not trust your data to a high capacity drive. MAKE BACKUPS. The higher the density, the more error correction required, the liklier you are to lose data.
Modern high density drives are CONSTANTLY error correcting. It's frightening. This is why I prefer using a small drive for the boot drive (I have a 74Gb Raptor as the boot drive on my main workstation, with a 500Gb spare drive for the data). Low density drives are more reliable. That's why I haven't jumped on the 1Tb bandwagon yet. I have 3 external drives: all 500Gb. The 500Gb drives are pretty damn reliable right now. Still, you never want important data stored in only one drive.
Some solutions are good old DVD (or DVD-DL) backups (Blu-Ray-RW when it becomes affordable), multiple drives, RAID Array NAS drives, or some sort of affordable off site backup like JungleDisk & Amazon S3.
Anything REALLY important I keep at least 3 copies of. For instance my MP3 library: there's one copy on my file server, one copy on an external HDD connected to my file server that gets synced one a night, and a third copy on DVD backups.