Here's an interesting Raid product. I've used enclosures and products from FireWireDirect before, and been very pleased with them. Usually well made, no-thrills, just plain reliable stuff at reasonable prices. An interesting feature of this enclosure is the lack of disk caddies, instead the naked drive is simply slid into a slot... It can be configured with all sorts of interfaces and options (like 3TB HDD and a blu-ray burner). 4TB eSATA (gen 2 SATA drives I think) comes out to about $1600, which is very competitive.

http://www.firewiredirect.com/categories/75/

Edit: by reliable I mean reliable relative to the usual PC stuff. Not Enterprise data center type of reliable...