HalloweeneBay's guide to sell products on Halloween http://for-business.ebay.com/aggressive-retailing-and-three-phases-halloween
Black FridayOnline merchants can take advantage of both Black Friday and Cyber Monday
There are subcategories of Christmas merchandise as well: stocking stuffers and white elephant gifts. These gifts are generally smaller, less expensive, and more creative.
Less obvious retail holidays
Summer is also a good time for juice, smoothie and cocktails.