To use for what ? I mean if its tunes youre after than as Johns_ar pointed out Soulseek is the way to go.
If on the otherhand you want games, apps, movies etc etc then reall the best option by a long way is Bit Torrent (
http://bitconjurer.org/BitTorrent/download.html)
combined with
www.suprnova.org for all your linkage needs
P.S Having just finished FIFA2004 and Silent Storm, I'm now downloading LOTR : Return of the king and Worms3D...ahh how I love Bit Torrent