Shareaza
Shareaza is a very new, and easy to use file sharing software tool that uses the peer-to-peer Gnutella Network. The interface somewhat reminds me of Napster.

Zeropaid
Zeropaid is the ultimate P2P file sharing portal with all the latest news and information on the best programs to download your tunes and files!

Bearshare
Bearshare lets you search for, download, and share files with everyone on the global Gnutella peer-to-peer information network. They have just released version 4.0 which is a big improvement in the interface and ease of use!

iMesh
iMesh is a search tool that lets you locate and download audio, images, documents, and video files from a growing community of seven million people.

LimeWire
LimeWire is a software tool that enables peer-to-peer file sharing on the Gnutella Network that's about as simple and effective as a Gnutella clone can get while keeping all the power of the Gnutella Network.