Absinthe's bar team selects the best places on the web to buy absinthe
AbsintheBuyersGuide.com - An excellent guide to buying absinthe and absinthe accessories on the web.
Absinthe Online - Yes, everything is priced in Pounds and has to be shipped across the pond, but they have a number of interesting absinthes listed that have yet to be made available here in the states.
Tempus Fugit Spirits - Bay area-based distributors/producers who only sell a few absinthes -- their own, of course -- but they make some of the best absinthe available in the US market. They're good friends of the restaurant, too.
La Fee Verte - This site is a sister site of the Virtual Absinthe Museum. It has a lot of historical information, as well as a good buyer's guide. Check out all of the links at the bottom of the page, as each is interesting and noteworthy in its own right.