We believe this list of Giganews Usenet resellers to be fairly complete.  If you see your Usenet provider on the list below, your newsgroup access is coming from a Giganews server somewhere:

Giganews airnews.net
Giganews giganews.com EU, US
Giganews powerusenet.com
Giganews rhinonewsgroups.com
Giganews speakeasy.net (ISP)
Giganews Supernews.com – EU, US
Giganews Usenet.net