RAID 1 & 10 are typically used for speed. The down side is you use half of your storage for fault tolerance.
RAID 3 is so uncommon I would avoid because if you needed to find a replacement machine to read that could be a pain.
RAID 5 & 6 are more common and widely used. They allow for the most fault tolerant space in that only 1 or 2 (RAID 5 & 6) are needed for parity information. RAID 5 you need a minimum of three drives. RAID 6 I typically see with five drives.
Also, if the files are large, I believe you will get better transfer speed with firewire than USB.
One more thing to consider is getting a controller or OS that allows you to use the drives fully. For example you have three 1TB drives and 1 750GB drives. Some controllers/OSs allow you to use 750GB across all four drives and then make a second RAID across the remaining three drive's 250GB. Otherwise you would loose 750GB of space.
As a side know I've heard many photo people speak their love for Drobo, many love the Drobo S because you can have five drives and it has eSATA. If you wanted an out of the box solution (and had the money), this may be a good fit for you.
I also agree with everyone talking about backups. Hard drive fault tolerance isn't a replacement for backup, but I don't believe that was in your question.
(I almost forgot, for all the ZFS lovers out there. ZFS have similar fault tolerance measure to RAID 5 & 6 call RAIDz and RAIDz2. I love ZFS because you can ensure the entegrety of the data and it had compression and deduplication. ZFS is available on OpenSolaris (no longer development), OpenIndiana (formed to continue OpenSolaris), FreeBSD, and Linux (via fuse and soon baked into the kernal).
FreeNAS is a great white box NAS software for RAID, iSCSI and the like, plus it is easy to setup. FreeNAS had ZFS as well, but the advanced versions of ZFS hadn't hit FreeNAS as of yet.
I also forgot to mention that ZFS does have a Mirror configuration.