Try this page.
All of these clients connect to the Gnutella network. Basically, just look at the screenshots and the description, find one that looks good, download it and try it out. If you don't like it, try another one. Whatever you download, though, don't download Morpheus. It's full of spyware, and it has lots of bugs which are bad for the network. The 3 best clients, IMO, are Bearshare, Gnucleus, and Limewire. Shareaza is also good, but it's aimed towards more experienced users.