are there really any large decent drives out there? I am looking for something in the 4TB range, just have not done much research on any particular drive other than to see the LaCie drives and how expensive they are?
If your mac had USB3 (I Believe the one in your profile does)...
USB3 is a bit slower than tunderbolt, but there are more options out there, and possibly cheeper.
USB3 is plenty fast for most home uses. Even USB2 can handle 3 or 4 raw Blu-ray streams at the same time.
If you're consistently moving very large files (read editing HD video all the time), then thunderbolt might be worth it, but to store a movie and music collection or to use for backups*, USB3 is fine.
to truly take advantage of the speeds of thunderbolt you'll need to load your RAID with SSDs
*just a reminder, RAID is not backup. always have a second copy of your important data somewhere else.