Mario Kart Wii
While it has not been made official, Daisy may be Luigi's romantic interest. They were a romantic couple in the "Super Mario Bros." film and in "Mario Kart Wii" they are seen in statue dancing together. She was his caddy in "NES Open Tournament Golf" as Peach was to Mario. Also on Daisy's trophy in "Super Smash Bros. Melee", it says that she is possibly Luigi's answer to Mario's Peach.