Both Amazon.com and Barnes and Noble maintain lists of new book titles in their stores. Additional lists of new book titles can also be found on publisher websites and in publications that review books, though these sources usually only list major new releases and not all new titles.
In general, new books from publishing companies are released on Tuesday, the same day that numerous other forms of media become available to the public. However, self-published books may become available any day of the week that the author chooses to release them. According to DearAuthor.com, the Tuesday release date is largely due to shipping and stocking convenience.