Usagi drop (real life, child adoption)
Kimi ni todoke (romance)
ore monogatari. (romance)
nisekoi (yakuza/romance) you already read it
Nana (real life, adulthood problems) but it's unfinished. we will probably never see the end. the Anime has a somewhat probable ending, not sure this is where the author wanted to end the manga. The author stopped releasing anything, while she had a lot of series. She's probably ill and can't draw anymore. You can read all previous series from her too.
I listed romance because you mentioned it, but that's only a very small list, there are so many manga you can just pick randomly !
get a list based on the story's genre and pick one.
or some manga from Saki Hiwatari, which I love. the author has her own writing style which might not be of everybody's taste, and always mix two story's time together (past/present, or present/future, real life/fantasy life, earth/other location (to not spoil), etc.) and characters have a connection in each.
Try "please save my earth" (PSME) or "global garden".
(don't start with reincarnation2, it's sequel to PSME)
her main genre is human relation and position in life, ecology and fantastic.
if you're up to horror, you can try Gyo, and other manga from same author (
junji ito) like the short "enigma or emigarata fault" to start soft.
(maybe too perverted, but not in a sexy way, more in a psychological mental illness way)
if you're looking for shounen, maybe Claymore.
or Gunnm (Battle Angel Alita), and Gunnm last order, which will have a movie adaptation at the end of the year.
more light hearted shounen ? Black cat.
or futuristic shounen ? Akira (soon! Olympic game at tokyo in 2020! he knew it in 80's right?)
looking for fantasy ? try Clamp's manga (RG Veda to xxxholic)
Sports series ? "Major" for baseball, but there are a lot more author I didn't read (foot, boxing, racing, tennis, etc.)
or any manga from Mitsuru Adachi. He has a funny habit : he re-use the
same chara design in all his series, but it's different people's situation and names. it's just the same design, not the same story. I'd recommend starting with his 3 "Short program" series. compilation of small stories of 2-3 pages.
or something different : Version (one shot), from Hisashi sakahuchi
edit:
please, let me know which one you tried, and what you though about it.
there are so many to recommend that it's not really a definitive list. like I said : pick randomly ! you'll be surprised