The end of the novel is a rebirth. Most obviously, it's the rebirth of the Hive Queen. For millennia she's been hibernating in Ender's luggage; finally though, she's out and laying eggs and stopping to eat the daisies. "Life, so long waited for, and not until today could she be sure that she would be, not the last of her tribe, but the first" (18.242). She's been in a half-life, for herself and her species, but now she knows she's going on. The book about trying to live with aliens (see the "In a Nutshell" section) concludes with the alien living. That's called a happy ending, y'all.
It's also a happy ending for Ender and Novinha. The two were married a few paragraphs back (18.229), and now Novinha says that they can "start to live" (18.240). So the Hive Queen (whose story Ender wrote), Novinha (whose story Ender spoke) and Ender himself are all united; the beginning of life for one is the beginning of life for all. To start life, you need the alien to start its life—which also makes the rebirth of the Hive Queen a metaphor for marriage, where alien differences (of a sort) are joined together to make a new whole.
Less romantically, you could see the ending as a metaphor for the Ender series. Like the Hive Queen herself, Speaker for the Dead is not the last, but just the beginning. There are two more volumes in the series, which continue the story directly—Xenocide and Children of the Mind. But even after that, there have been nearly a dozen more volumes about the Ender's Game universe. The Hive Queen isn't just laying eggs, folks—she's laying books, which will scrabble chittering out into the sunlight as fast as Card can write them.