[quote="coffeehubby (post: 1314220)"]I have seen ( and loved): Spirited Away/ Howl's Moving castle/ Laputa, Castle In The Sky/ Porco Rosso ( favorite)/ Princess Mononoke/ Nausicaä]
Fixed it for you
Not trying to be a pompous jerk (though I've been called that), just so you'll know better if you ever need to look around related stuff.
Anyway, to answer your question: The other great director in Ghibli is Isao Takahata who maintains a sort of friendly rivalry with Miyasaki. I think most people will agree with me that The Grave of the Fireflies is his Magnum Opus and is definitely a must watch (just keep in mid to have close to you a box of tissues.) His other films with Ghibli are Pom Poko which you already mentioned, Omohide PoroPoro (Only yesterday) which is very recommendable as well, very mature (in the good sense) and My Neighbors the Yamata, a light-hearted family comedy with cartoonish animation. His most notable pre-Ghibli works would be the immortal classic series Heidi: Girl of the Alps and the movie Hols: Prince of Sun.
As for Miyasaki, if you want some other pre-Ghibli stuff you could check the movie Lupin the 3rd: The Castle of Cagliostro and the series Nadia: Secret of the Blue Water which he created but was directed by another (at least IMHO) genius director, Hideaki Anno. The old series you are thinking about is called Future Boy Conan.