1. Fruits Basket: This series is my favorite series of anything that has ever been written and I honestly believe that no other series will ever be as perfectly written as this one was. Fruits Basket is a series that just has so many great characters and relationships and pretty much the entire series is about how those characters and relationships develop over the course of the series. I love that this series is one that starts out light but then gets darker later on but the story ends on happy and hopeful note for the characters. This series is great if you haven't read it you should because it's a wonderful story that will teach you to be a better person.
2. Tsubasa Reservoir Chronicle: This series is one that has the main characters traveling through dimensions which is a concept one does not see often which makes the series stand out from the beginning. This series is one that has great characters that I can't help but to love and really great romance that almost broke the space time continuum so that right there shows you how powerful their love for one another is. The series also has great art since it was created by Clamp.
3. Cardcaptor Sakura: This is another great series by Clamp and this one is about a ten year old girl who has to capture these Clow cards in order to keep her town safe. This series is really sweet and fluffy and at it's core Cardcaptor Sakura is a story about love in all its forms and it's just a series that always makes me happy.
4. Tokyo Babylon: This series is also by Clamp but unlike Cardcaptor Sakura this story is not a happy Story in fact it's a tragic story. This series has young man that has magic powers and uses them to help people who he believes are generally good and kind at heart and through his job he sees what people do at their most cruel and selfish points which starts to chip away at his optimistic outlook on life but nothing hurts him quite as much as falling in love, it doesn't end well.
5. Gakuen Alice: This series is a story about a young girl who runs away and joins her friend at boarding school for gift children and while the story starts off fairly lighthearted things getting darker as the series goes on and more about the school is revealed.
6. Chibi Vampire: This series is a coming of age story for a young girl who is a vampire who is a reverse of what a vampire should be in that she produces too much blood rather than needing to drink blood. The series is delightful and quite a fun read with likable characters and interesting mythology.
7. Shugo Chara: This series is a magical girl series which is my favorite sub-genre of manga/anime and this series deals with a girl who puts on a false cool girl image but is forced to confront her other would be selves by her guardian characters who help her save other kids around age from loosing their dreams, the premise of the series doesn't make a whole lot of sense out of context but I assure you this series is great.
8. Rosario + Vampire: This series is about an extremely average boy that accidently gets sent to a school for monsters and ends up unwittingly winning the hearts of quite a few of his female classmates by simply being nice to them. This series can be a bit out there but it's great fun to read.
9. Pandora Hearts: This series is a very different take on Alice in Wonderland that deals with a young boy being taken to a sort of underworld only to be saved from that world by making a deal with Alice who is someone who lives in that underworld. This series is a bit hard to sum up but the story and it's characters are really great.
10. Magic Knight Rayearth: This series is a magical girl series about three girls who get transported to another world to save it's ruler and become great friends with each other through out the series. This series has great art, good characters, an interesting plot and killer twist at the end of it's first series.