There are a few threads like this where I've said the same thing, but here's another vote for
BitTorrent and
eMule. BitTorrent is one of the best ideas out there, especially for fast transferring of new content. By design eMule and especially the new experimental serverless sister client Kademlia (Kad, which comes enabled by default on the new emule) will have the most longevity.
Torrents are usually more short-lived -- they rely on a lot of participants, popular content, and the reliability of servers. They also tend to be faster since all participants are constantly active. Sure eMule is slow compared to BT, but the fact that you get credit for uploading and often end up uploading more or just as much as you download ensures that content won't die. It's also got a rating system to flag fake or foreign-language content which is cool. And Kad is bad ass -- it doesn't rely on servers, as every participating client acts as a mini-server that each does a small part. You can read about it here, the design is very well thought-out:
http://en.wikipedia.org/wiki/Kademlia