Apt-p2p gives you the ability to download Debian packages via a peer-to-peer protocol. Apt-p2p will try to get the packages from peers before it resorts to pulling them from the repository. More here
This saves bandwidth for the repository servers, can speed up your download speed, and ads to the sense of community which Debian is so rich with. Downloading and installing Apt-p2p is pretty simple and can be done via apt. Take a look at the main apt-p2p page for download details.