Ai Yori Aoshi
Just to get things rolling, I'm going to start off with Ai Yori Aoshi.
I just love this series, well, I love the Manga more then the Anime to be more specific.
The artwork is amazing and just keeps getting better and better as the series progresses (Aoi keeps getting cuter and cuter).
Some aspects of the storyline is a bit on the corny side, but the core of the story stays true to the theme through out: A love story between two people whose families dissapprove of their relationship, and how they cope with this adversity and grow closer while doing so.
While the anime is decent in its own right, it does not cover the whole story, so the manga really is the better choice. The story is expanded much more fully, Characters are more fleashed out and because of that, you care for them more.
This series isn't for everyone though, you have to keep in mind that this is a Harem anime, and as such, there is slapstick comedy, echii, and in the manga, nudity and sexual content (Think soft core here folks), and because of this, I wouldn't let children read this.