Michael Corner is a Ravenclaw student, member of the D.A. – and Ginny's boyfriend for about half of Book 5. He seems like a decent enough guy, but his very presence totally freaks out Ron. When Hermione mentions off-handedly that they're dating, Ron shrieks, "But [...] I thought Ginny fancied Harry!" (16.195). Hermione explains, "Ginny used to fancy Harry, but she gave up on him months ago" (16.196). Apparently, Ginny and Michael got together at the end of the previous year after meeting at the Yule Ball.
Michael Corner is also a Ravenclaw Quidditch player. When Gryffindor beats Ravenclaw and wins the Quidditch Cup, Michael is so huffy that Ginny dumps him. Michael moves on to Cho Chang (who is, of course, the Ravenclaw Quidditch team Seeker). This means that Michael Corner has dated both Ginny and Cho Chang – his romantic interests are startlingly close to Harry's own.