I believe Tom Riddle, Jr. (aka Lord Voldemort) qualifies.
Merope Gaunt had Tom Riddle, Sr. under the effects of love potion (or at least that is what Dumbledore and Harry believe). They were technically married, but Tom Sr. had left Merope prior to Tom Jr being born.
We see the following quotes in The Half-Blood Prince
Albus Dumbledore: "Can you not think of any measure Merope could have taken to make Tom Riddle forget his Muggle companion, and fall in love with her instead?"
Harry Potter: "The Imperius Curse? Or a love potion?"
"Tom Riddle left her while she was still pregnant... I believe that Merope, who was deeply in love with her husband, could not bear to continue enslaving him by magical means. I believe that she made the choice to stop giving him the potion."
"Within a few months of their runaway marriage, Tom Riddle reappeared at the manor house in Little Hangleton without his wife. The rumour flew around the neighbourhood that he was talking of being 'hoodwinked' and 'taken in'... He left her, never saw her again, and never troubled to discover what became of his son."
An "out-of-wedlock" birth literally means children born of a mother and a father who were not married at the time of birth. If we take a strict definiton of the phrase I feel Tom Jr qualifies because even though Merope and Tom Sr were married when Tom Jr was conceived, they were not married when he was born.