Love Roma
Yume de Aetara
Gonna say Emma too, it's fantastic

Didn't include oneshots and tried not to repeat what was suggested. This are only (mainly) what I myself have read.
I really recommend you start on CLAMP works. They are a group of four with many manga published. The world they've woven is incredible, and there's a connection with their stories.

Your taste is quite different from mine, but here are ones that I enjoyed:
Ouran High School Host Club
Nousatsu Rock Shounen
Boku wa Kisu de Uso wo Tsuku
Beauty Pop
Lovely Complex
Ai kara Hajimaru
Atashi wa Bambi
Kimi wa Pet (My fave romance so far I think... I think you'll like it too)
Strobe Edge (Another fave... but quite cliche)
Shugo Chara!
Cardcaptor Sakura
Sugar Sugar Rune (I reckon had great potential...but the plot actually went no where for me and it was kind of a let down)
Nagareboshi Lens
Fruits Basket (actually I've never read but I know it's a classic)
Nodame Cantabile
Hachimitsu to Clover
Kodomo no Omocha
Nana (I think you'll like this one)
Usagi Drop (Haven't read)

Most of what I read are romance I realize.... or else good shounen are just never-ending...
Either way, these are ones that fit you criteria, are pretty good but personally not my type (some are still highly praised works, just a matter of taste):
Love Berrish
Aishiteruze Baby
Shinshi Doumei Cross
Koibana! Koiseyo Hanabi
Mishounen Produce
Ageha 100%
Full Moon o Sagashite
Bokura ga Ita (Haven't read and don't like)

Awesome, again! I've read a couple of CLAMP manga. I guess I should check out the rest!

Thanks!

some of my all time favorites have been
Marmalade Boy
Akuma De Sourou
Kodomo no omocha
Immortal rain
Kitchen princess