I've used tape backup drives, but they're pricey for personal use and slow as molasses. The small firms I've worked with (or helped start) prefer hard drives for efficiency and speed, and are cheaper than they've ever been. For personal use, hard drives are the way to go. DVD's have not proven to be shelf-stable for long periods of time, and they're too small...one backpacking trip can more than fill a DVD-ROM if you shoot Raw.
If you take so many photos that you use a digital asset management tool like Lightroom, then you've got a database to back up as well, and that gets even more sick 'n' twisted.
Me? I first store all photos on a mirrored RAID - that way I get automatic redundancy. Then, weekly I clone that RAID to another RAID of identical size (there are many free and cheap utilities to do this). For my non-photo, non-work stuff, I have an automatic tasks to clone my laptop's hard drive to another external hard drive. Yep, that means for one computer I have 5 to 6 hard drives. :-\ Kind of insane but piece of mind is everything.
So far so good, but it's not disaster-proof: I have no long-term, OFF-SITE storage for everything (I generate 200+GB of media per year between work and play). The photos I really care about I render at full rez and upload to Flickr, but they're just JPEGs, not the RAW originals.
Short version? Always buy hard drives in pairs!