Long-term backup storage media

Hard Drives. Space is dirt cheap these days, you can grab a few TB worth of internal hard drives at a fairly low price. Even external hard drives aren't too expensive.

Regarding longevity, you'll probably accumulate data too fast for the media to be a problem. 7 years from now you might have enough DVD's to fill a couple Blu-rays. 7 more years and you'll have a stack of Blu-rays ready to consolidate on whatever the next big thing is.

For now, Patrick McFarland's How To Choose CD/DVD Archival Media comes out in favor of DVD+R, specifically Taiyo Yuden's:

To begin with, I do not recommend CD-RW, DVD-RW, or DVD+RW media in any form for permanent storage. This is mostly a no-brainer, but those discs are meant to be able to be changed after burning, and they are simply unsuitable for long-term archival storage. I also do not recommend DVD-R media due to DVD+R’s superior error correction and burning control.

That said, I recommend Taiyo Yuden media across the board. Taiyo Yuden currently manufactures 52x CD-R, 16x DVD-R, and 8x DVD+R media in normal shiney silver, inkjet printable, and thermal printable forms. Taiyo Yuden may be one of the most expensive (if not the most expensive), but their media quality is unsurpassed.

A recent update shows he still affirms this position.

I thought I read somewhere that the Library of Congress uses MAM-A archival gold DVD's but considering the cost I stick with TY's. I usually purchase through http://www.rima.com, while McFarland recommends another vendor in his article.

I'm not sure hard drives are any better than CD/DVD long term. The only way to be really sure is to keep checking the data and refreshing it. There are CD's/DVD's that are specifically designed for long term storage but as always these are more expensive.

I think it has to do with how much you're willing to spend. I've thought about this in the past and the best solution I could come up with was a NAS with 2 large HDDs in RAID 1 configuration. This way you're protected from HDD failure and I'm pretty sure that Ethernet will still be around 10 years from now. Only worry is if the NAS itself breaks down, so you'd need a quality one.