If you aren't a plexpass member I'd grab that before the lifetime membership goes away. The pre-release stuff and plex home theater is pretty great. My only issue is that I haven't gotten it to work all that well with my Roku 3 yet. Not a big deal, but it would be pretty cool to have that little $99 box play all my bd's instead of having to have a HTPC front end.
I'll mention unRAID since nobody else has. It can run plex as on of it's apps and also supports all kinds of other things. It is a software RAID solution which for me is great just for the simple fact that with a hardware (or intel software RAID) raid card you run the risk of the actual card dying and having issues rebuilding the array with the same model of replacement card or trying to find one that is compatible. I've read some bad things about the on-board motherboard RAID being a problem if the board dies. You can't rebuild the array.
With unRAID, as long as the version is compatible you can rebuild your data without issue. I've had this discussion with my on-site guy (I'm not a server admin anymore, so I'm a bit behind on current business trends) and he says RAID 5 and 6 are "old" and outdated. They use RAID 10 now. Granted, you're talking much larger storage needs, and much higher speeds, but it would be fun to play with.
RAID 5 and 6 are great, it just depends on how much parity you really want. unRAID is essentially raid 4 where like RAID 5 you have single drive parity, but it is on a single drive as opposed to spread across all drives. The benefit of unRAID is that even if you have a dual disk failure (which in RAID 5 you are pretty much screwed, RAID 6 you're good) you can still save the data off the drives that are ok as they can be read by any linux distro (basically you would use a UBCD or something linux based to get your data, pretty easy). I don't know of another solution that has that capability.
Another good thing about unRAID (like flexRAID) is that you don't need expensive hardware controllers to have large arrays. You can get a normal SAS card (SATA compatible) like
this one that supports 8 drives including over 2tb drives. Only $110. Lots of future expandability.
Ok. I'll stop now, but this is a fun project when you're building, and when you're done it just works. Pretty awesome.