Like School Rumble, Fruits basket, and Vampire knight.?
Fushigi Yugi. Chobits. Fruit's Basket. Peach Girl. Ouran High School Host Club. Gakuen Alice. Elfen Lied. His and her circumstances. This Ugly Yet Beautiful World. Paradise Kiss. Gravitation (boyxboy) Escaflowne. Record of the Loddos War.
If you like yuri, the love triangles I can think of is Kashimashi - Girl Meets Girl which is quite funny and cute and Strawberry Panic's love triangles are just brilliant. I only really watch yaoi and yuri so.. tada xD
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Inuyasha! Lol Very founder of love triangles lol the only reason i say that is cuz it was my first anime
Cherry juice and lolipop and shugo chara shugo chara is my absolute favorite:)