SuperNZB ^tm
The Newsgroup NZB Downloader

In the screenshot below, you can see SuperNZB (which looks identical on the Mac) finishing up a 1.16gb set of RAR and PAR files in about 35 minutes. Using the six connections that come with a TechSono News Service account, and a common 5mbps cablemodem, it averaged a speed of 4,567Kbps with a peak at 7,112Kpbs (due to hardware compression in the modems.)