Don't buy Dell drives from Dell. Buy them from resellers (xbyte, serversupply, etc.) - same drive, half the price (or better). WD has certified the RE4 on most Dell controllers. If getting drives that are not certified by either Dell or the manufacturer, then just stay away from power-savers, desktop/laptop, or NAS drives (I.e. WD Red, Green, etc.). Also, using non Dell-certified drives does not void the server warranty. Dell won't usually troubleshoot storage issues if you have non-certified drives, but any other issues are still fully covered.
I've recently purchased a T320 which I'll build into a home Server, to fulfill a variety of roles (media server, file/print etc.) It's reasonably basic, and has the H310 RAID controller and 8 3.5" hot swap bays. I'd like to put together a reasonably robust RAID 5 array in the thing, using decent sized (4Tb) SATA drives which won't have the RAID controller having fits. My thinking was something like the HGST Ultrastar 7K4000 drives (model HVS724040ALA640 or HVS724040ALE640 - what's the difference between these?) or something similar. Not interested in paying the exorbitant prices Dell wants for their compatible drives, so was wondering if people have suggestions for Enterprise drives which are certified to work in the box? The HGST drives mentioned above are supposed to be certified to work with the T320s, but some real-world experience/advice would be handy... Note: This is not a mission-critical production box, and will be backed up regularly (to an HP Microserver box), so Dell warranty etc. isn't critical to us. Would appreciate some advice from more knowledgeable consumers of these things... 
T320 Server Enterprise HDD options?