My Gouldian Aviary - fantastic site, lots of information and a great forum.
Andrew's Bird and Pet Palace - members only site, but worth joining up.
Clifton Finch Aviaries - most useful site I have come across.
Queensland Finch Society - interesting site.
Australian Bird Keeper Magazine - great magazine.
Bird Health - Site by Dr Rob Marshall.
Phils Feathered Friends - one of the best forums I have been to.
Lady Gouldian Finch - an American site, but has a lot of great information.