Whatever you do, avoid the Seagate 320GB (38% of newegg reviewers hate it, it dies a lot). Also avoid the WD5000AAKS (no PMR, it hurts the average R/W rates).
The WD6400AAKS is pretty similar in speed to the Seagate 500GB, maybe a bit faster (90MB/s avg rates). It's also cheaper per GB. It has only 3 years warranty (Seagate has 5). One of these models sounds best IMO.
Edit: OK, maybe I'm too harsh on the WD5000AAKS. I have 3 of them, and they still work perfectly after more than a year. And the difference between 74 and 90 MB/s is not really that big. I wouldn't buy more of them now, but you can keep the one you got without worries, it's a good disk.
No, WD gives only 3 years on a lot of their models.
I don't think it really matters for a home user. At least my WD disks never died, and I did use some of them for as long as 7 years.
Based on a Google study, I think the numbers were like 28% of HDDs died in the first 3 years and another 15% in years 4 and 5. That is, with Seagate 15% of disks actually benefit from that extended warranty. (The numbers may be wrong, it's been a while since I read that). But, those were Google's disks, extremely heavy usage, not like the normal HDD on a home computer.
whatever you get, avoid the Seagate Barracuda 7200.11 ST3500320AS 500g (especially the SD15 firmware). it just dies a lot for no apparent reason (faulty firmware or smth). search the web for more info if you're interested. also, if you have one already, be sure to backup your data often.
if i shouldn't have posted here (because it's some 4 months late), sorry. my first post
Forget the Seagate ST3500320AS it dies for no reason or arrive with crazy performance problems.
In 3 months i already shiped two of that first came with crazy performance problems (1Mb/s on read test? 70-120ms on random access time?). The second one (returned after the trade from Seagate) died 2 months later for no aparent reason.