Barnes & Noble and Amazon won’t let us indie authors upload free books directly to their sites, but there are some back doors. If you upload your freebie at Smashwords, such as I did with my fantasy short story Ice Cracker II, and click the “distribute to B&N” option, the ebook will eventually make its way to their store (you can check this button for Amazon, too, but it sounds like you’ll be holding your breath for a while).
I have also heard of people getting their ebooks listed for free at Amazon by uploading their ebook for $0.99 at Amazon while listing it for free with Smashwords. Since Amazon price-matches, they supposedly will eventually get the price dropped to free.
I may try this with Ice Cracker II, though it’s only a short story (about 6,000 words), so I’d hate to list it for a buck at Amazon. We’ll see.
In the meantime, give it a read at B&N or Smashwords (kindle and epub versions here) if you like fantasy!