SYNC is showing its list of free summer downloads.
I don't see a dedicated page yet, but the navigation bar shows "SYNC'13 Classic Titles" and "SYNC'13 YA Titles." Under each one there's a drop-down list of the books; you can find descriptions and dates of free availability for each of the titles.
It's early, but I just thought I'd mention it in case someone's planning to purchase a book that will later be free.