The best store bought chai I have ever had comes from Nub Chai. Easily.
You can buy their concentrates online. They've been a sort of underground favorite in the Bay Area for awhile, showing up at early-era dot com parties and the like. Far as I know they are stll going strong and elarging their offerings. You can also by their packs of spices and brew your own.
It's all organic, too.
They do retail and wholesale. Can you tell I just love them?
What nailed it for me though, was a night at Burningman in their tent out on the playa. They offered free nub chai the whole week long, it was a true oasis in the desert, down to the artistic fountain they somehow created out there in the middle of nowhere in the center of the tent. We sat around at 2 am on pillows drinking warm chai and sucking on sweet orange slices...oooh my oh my.
website for nub chai:
http://www.nub.com/nub_main.html
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SlaveGirl
http://www.restaurantslave.com