- USA: see the Wormwood Society below. Also various Tribes, MySpace and Yahoo Groups, etc.
- UK: Fee Verte. A forum and buyers guide.
- France: L'Heure Verte. Lots of information and smaller forum.
- Germany: Absinth-Guide. Lots of information and forum.
- Netherlands: Groene Fee. Information and a smaller forum.
- Italy: Sifattack. Less absinthe focused forum.
- Russia: AbsintheClub. Seems good, but I can't comment too much since I don't understand it at all!
- Poland: Absynt Forum. Comment as above.
- Belgium: Muse Verte. Comment to follow.
- Japan: allegedly!
and those are just the ones I know about. Many of these have hundreds of members, and a few have thousands of members. However, let's not confuse quantity with quality, or ease of getting information for those just starting on their absinthe journey.
For me, one of the best resources is the Wormwood Society and its forum. It's not the biggest absinthe forum in member numbers, but it's very active, the discussion is good, the members are fervent in their desire to help people, and they are a great group of people. Most importantly, they seem to have a passion to do the right things to get absinthe legalised in due course in the USA.
Some other forums may not provide such a warm welcome for new members!
And let's not forget Wikipedia: the main editors of the Wikipedia absinthe article have done a great job compiling an article that was Featured Article of the Day on June 20th 2006, and remains at the time of writing the only alcoholic beverage article so honoured.
Some other resources are partly or largely gateways to vendors promoting Czech absinth. Buyer beware!