I like most of the Rumiko Takahashi series I've seen/read....most of it is extremely funny,though Mermaid Saga and some parts of Inuyasha prove she can also do horror quite well....
Ranma 1/2...One of the funniest manga I've read (along with Tomoko Hayakawa's The Wallflower and Tite Kubo's Bleach)...the anime is alright,but not quite as funny...
Maison Ikkoku...a bit slow in places,but overall a great romantic comedy series...and has one of the best endings I've read in a manga...I've only seen the first 36 episodes of the anime (since Viz only sold the series online after the first 3 boxsets)...
Inuyasha....Even though the series is long and can get repetative,it's never failed to hold my attention....I like both the anime and manga equally...
Mermaid Saga....Somewhat of a departure for Takahashi,this one's a horror series (with very little humor) involving the nature of immortality....It's an interesting read,if you can find it....there's also a TV series,which follows the manga pretty well....
One-Pound Gospel....Just finished reading...it's a comedy series about a boxer who falls in love with a novice nun...it was cute,and fairly short (4 volumes)....