Stuff similar to kare kano, Angel Sanctuary, or Fruits Basket. I just got into shoujo so you guys can probably recommend me a ton of stuff.

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Bara no Tameni
Kanata Kara
Koukou Debut
Mars
Miriam
W-Juliet

A rather eclectic list...

I'd probably suggest different manga for different ages, like when I was in my early teens (now I said that I feel so old...) I really liked Koge Donbo's works such as Kamichama Karin (I'd use the direct link thingy but I don't know how to, so more work for you, sorry). Another work for younger teens I recommend would probably be Aishiteruze Baby. Shugo Chara is also a possibility, it's drawn beautifully but the story can get a bit repetitive.

If you're a bit older ... it's actually quite hard for me to think of some as I've read too many... I guess I'll just mention some popular ones (not saying they are the best, but a lot of people like them so I guess you would be more likely to): Skip Beat, Vampire Knight, Gakuen Alice, Kimi ni Todoke, Special A, Ouran High School Host Club - these are probably like the Narutos of Shoujo manga...

As for ones that are exceptionally good, there probably aren't any, all the mangas I have read had their good points and many many cliche points... but I still enjoyed them. Anyhow, some not-so-popular (but still well known) manga that I liked would probably be Koishi Tagari no Blue, Strobe Edge, Dengeki Daisy, Oboreru Knife, Kodomo no Omocha (I usually don't like old manga but this one quite cute) and I'll also add Ghost Hunt though you can't really see a lot of romance in that one.

Shuukatsu!! - Kimi ni Naitei
Yes... I'm spreading this one like wildfire (if possible)... though... I guess it's more Josei/Slice-of-Life? No hormones here... just a nice, slow, college romance... left me feeling good (like Fruits Basket)

Ouran Koukou Host Club
Everyone loves the heroine. Reverse harem. Think Fruits Basket but no Zodiac curse and a lot of laughs. Last chapter comes out the end of this month!

Shiawase Kissa Sanchoume
Life centered around a cafe/bakery. Oblivious love. Not sure about scanlations being continued as of now...)

Special A
Similar to Kare Kano I think... (I only read the first chapter, and it's on my On Hold List

I'm not sure what else... but @Eeeeh basically listed the English licensed "Naruto's" of Shoujo manga... Been fearful of picking up long volume shoujo's, so I'm sorry for the short list...

I'll juz list my fav....

Akagami no Shirayukihime
Akuma to Love Song
Dengeki Daisy
Kaichou wa Maid-sama!
Kimi ni Todoke
Kingyo Sou
kiss
Karakuri Odetto
kirai
Oresama Teacher
Perfect Girl Evolution
Reimei no Arcana
Say I Love You
Shiawase Kissa Sanchoume
cat street
crossroad
Yesterday o Utatte
Zettai Heiwa Daisakusen

there is too many, mayb you can check my complete list for other chioce.....

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Come back if you have a request more specific. [: