P2P is at it's finest these days. With the invention of Bit Torrent Clients (often spelled Bittorrent), P2P sharing has evolved into something spectacular. What you aren't able to find on the normal P2P clients (Kazaa, Bearshare, Limewire, Grokester, etc...) you can find on Bit Torrent networks. Not only are you able to find more of what you can't find on Filesharing Networks, but you have a better chance of actually downloading the files. Before I get into why this is, let me show you how Bit Torrent clients work (taken from http://bitconjurer.org/BitTorrent/introduction.html)...
A normal computer server can only serve so much information to computers.

But P2P clients help to solve the problem of bandwidth limitation by having the customers share information with each other.

Now here is how Bit Torrent differs from regular P2P networks. Clients such as Azereus read a Bit Torrent file (which you can download from many different web pages) and search for others sharing that Torrent. Think of the torrent as a bookmark for filesharing. Then as you are downloading from the Torrent file, it puts together small pieces of the file starting with the rarest files.
Azereus is the client that I am currently using, it allows you to pause downloads, reorganize the files, set download priorities, and view the download status (which is a really impressive feature). For more information about what Bit Torrents are and how to use them please visit these sites:
Bit Torrent FAQ
What's so great about Bit Torrent's?
Azerues Bit Torrent Client