I don't know if I would said the PERC 5/i is the best RAID controller around, but it is the best bang-for-buck RAID controller. I got a card, battery backup, and cables for $100 shipped. Haven't regretted it.
Would this array be for storage or will you have your OS on it or something? I would consider getting the WD green line if it is for a file server, only because greens are cheaper, uses less power/doesn't get as hot, and performance will probably be bottlenecked by the network anyway. If you already have the black drives, the 5 year warranty probably wont hurt...
I think one of the biggest things that lead me to purchasing a PERC 5/i instead of using a solution like FreeNAS is because of being able to expand existing arrays. Plus, I like how I can run Windows on it without having to dual boot or something. I like know I have a backup computer, since my laptop's XP installation crapped out the night before a final while I was studying (many of my notes were electronic).