Shuffle!
Da Capo
Canvas 2
Gift ~Eternal Rainbow~
Kimi ga Nozomu Eien
^The above 3 are love triangles instead of a harem. Shuffle is the only true "harem" among these. Da Capo is the second closest, though this is also a love triangle rather than harem - although there are many girls who like the guy, it is clear from the start that only 2 of them has a shot at the guy's heart. The last three are triangles instead of harems.