Recommending some all-ages and female-oriented series. They don't have the most beautiful of art, they're mostly focused on the storytelling and some are older works.
Basara and Please Save My Earth are probably my two favorite manga with romance, adventure, and some mystery. Sadly, both have long been out of print in English despite success in several countries. If you can get a hold of the first few volumes of either series they're well worth reading.
From Far Away by Kyoko Hikawa is available in English. It has violence but nothing too graphic. Romance/adventure with an old-fashioned aesthetic.
Twin Spica is one of the most heartwarming and wholesome drama with several adaptations. The manga is available in English and on the Kindle.
http://www.amazon.com/Twin-Spica-Vol...mm_kin_title_0
Karakuri Odette is one of the few comedy series I've found that has a very cross-cultural sense of humor. Honey and Clover and Sand Chronicles are two other more recent series with nice art and thoughtful writing, very focused on drama. I would also second the recommendation for Nausicaa by Hayao Miyazaki, a sprawling adventure with a fantastic heroine.
Also this one-
http://www.amazon.com/With-Light-Rai.../dp/0759523568
I have way too many to recommend so I'll just stop here.