I second Tatta Hitotsu no koi
You Who Came From The Stars: well obviously he's not exactly ordinary since he's an alien, but to everybody else he's a normal guy, and she's a superstar
Queen In Hyun's Man: same case as the previous, only he's not an alien but a guy from the Joseon era :p
Que Sera, Sera: the rich girl does fall for the ordinary guy but... it's kind of twisted. I can''t tell more because I don't want to spoil the drama, but let's say the drama isn't a pleasant romantic story about how the ordinary guy gets the amazing girl...
My Sassy Girl (movie): she's not rich, but she's rather extraordinary, while he's painfully normal
I think it may also be the case with dramas like Witch's Romance and especially Secret Love Affair, although I can'tbe sure since I haven't watched them