The Apple I went on sale in July 1976 and was priced at $666.66.
While You Were Out: Apple's Years With and Without Steve Jobs, in today's New York Times.
Steve Wozniak on how they arrived at the price point:
I simply like triple digit numbers with all the things I'm involved with, the cost of making the Apple 1 was around $540 or there abouts and we agreed on the best markup, retail price above the cost of building it, which worked out to $666.
Jobs then tacked on the 66 cents to make it an eye-catcher price for the ads with the sale and promotion publications of it to the public.