I heard Unison is the client of choice. It costs but there's a cracked version floating around on various newsgroups.
Info about unison
http://www.panic.com/unison/
More mac clients & programs related to Usenet
http://www.pure-mac.com/usenet.html
Also there's a free client called OSXNews. Here's the URL http://osxnews.sourceforge.net/new2/
