Comment My solution - Raid 6 (Score 2, Insightful) 609
You don't specify what constitutes lots of data. In my case, 2 years ago I went for 6 750GB SATA drives in a Raid6 configuration. There's some very good posts here about some lesser known data reliability options, but personally I wanted to go with a worldwide standard that had been around for a long time and wasn't reliant on a couple guys hacking code in their spare time to make disk redundancy and file access work.
I bought a standard full size tower case, got a very large power supply, and spent a good deal of money on a mid-tier Raid controller. My primary requirement was Raid 6 so I could lose two drives without losing all my data, and my secondary requirement was having true hardware raid support. Most Raid controllers that are not enterprise business class are not true hardware raid - meaning that they use software and the CPU for some of the operations. This slows down file read/write. I did the research and read reviews and got a decent Promise card - if you have the money, go for LSI, Areca, or 3ware. Next, I got a Promise hot swappable 4 drive SATA bay. Not really sure why, it doesn't serve any purpose since in 2 years I haven't had a failure and thus have not had to hot-swap a drive. A very important thing is that I also purchased 7 drives for my 6 drive setup. So I already have a spare if I need it, and I don't have to worry about having the spare cash when a drive fails, or waiting on an RMA if it was still under support, etc. The one thing I wish I had done, and still might, is buy a spare raid controller with the exact same chipset. If your raid controller fries, ALL of your data is gone unless you can get the array up and running on an identical controller. That's a freaky thought!
6 drives in raid 6 at 750GB gives me a little under 3TB of disk. I wanted that in a single partition for ease of use, so I messed around with some 64 bit Linux distributions and did not have any luck. I finally settled on Vista of all things, but only after I got fed up with fighting with Linux - I didn't give it a fair shot, I should have been able to make it work. The only thing I can think is that it didn't like my controller or motherboard.
So, 6 drives of 750GB in Raid6 gives me 3TB. At the time I had less than 1TB of stuff, and wanted to make sure I had room to grow. I didn't grow anywhere near as quick as I expected, and I'm still at less than 2TB today. 2TB drives in a raid6 would give you 8TB, and that's if you only used 6 drives - you could easily add more into that same Raid6 array (depending on how good your Raid controller is). Even if all of your movies are dual layer quality, say 6GB each, that's over 1300 movies. That'd certainly last me a long time!