We've known this can happen in captivity for a few species of lizards, snakes, sharks and birds—when females had been kept away from males entirely—and is not uncommon for wild invertebrates.
Perhaps it need not be said, but this is nearly too cool for words.
BBC News reports that scientists caught several female copperheads and cottonmouths, and when they gave birth the young were genetically analyzed. Of the 22 copperheads, at least 1 had given birth without having eggs fertilized by a male. One of 37 cottonmouth litters was similarly born.
Professor Warren Booth, who conducted the research, says that the apparent 2.5-5% rate of virgin birth is "quite remarkable for something that has been considered an evolutionary novelty."