We already have an anime thread so a manga thread is essential.
I've not bought much in the way of manga for some time, because it's so hard to know what is good and what is teenage junk. And with a series running over so many books it can be intimidating to take the first step. So here's a place for your top manga recommendations.
I'll start off with:
Nausicaa of the Valley of Wind.
Far, far better than the anime, this is the Lord of the Rings of manga. Miyazaki-san is a beautiful illustrator and I wish he's draw more manga.
Urusei Yatsura
Crazy, hilarious, marvellous characters. Rumiko Takahashi at her best.
Maison Ikkoku
Another Takahashi series, it's the template for so many manga and anime that followed. The story is funny, touching and dramatic at times. It actually had a conclusion, which is nice because so many manga just go on forever.