Parthenogenesis

There is nothing inherently Christian in the origin of the virgin birth. 

Isis & baby Horus. Osiris is betrayed by his brother Set and murdered. The different parts of his body are spread around Egypt but Isis manages to get hold of his phallus in order to give birth to Horus the sun god. Similar to the Christians there's the muddled idea that the son and the father the same person who died in order to act as judge of the dead in the duat (underworld)

Devaki & Krishna, the Greek word for Cristos comes from the Sanskrit root Krsna.

Leto & the sun god Apollo. Zeus got Leto pregnant. She was an outcast and had to travel to various places until she finally gave birth on the island of Delos. You may think I've forgotten to mention Apollo's twin sister, right? In many versions Artemis is born fully grown.... and even helps out in the birth of her brother! Feminists have a lot to say about this one! 

Semele/ Zeus & Dionysus. This one is even weirder. Again, Zeus is up to his old tricks but this time his wife Hera gets wind of his latest fling and decides to take revenge. She tells Semele that if her lover really loves her he will come to her in his true form. Zeus, of course promises but soon regrets having done so as when he comes as pure lightning the heavily pregnant Semele is fried. Zeus takes his son and re-gives birth to him himself. Thus Dionysus is known as the twice born or resurrected god who has a special knack for changing water into wine.

Messalina & Britanicus (son of the deified emperor Claudius) although not technically a virgin birth it is this one that was the main inspiration for the later Christian imagery.