For most Ghibli movies there are so called "film comics " ( e.g. for Princess Mononoke ), which are graphic novels and similar to a manga.
As for other Ghibli-like manga, it might depend on what is meant by "Ghibli-like".
If it's steampunk technology , mixed with fantastic or magic elements (e.g. Castle in the Sky, Spirited Away) you enjoyed, here are examples for well-known manga which have these, too (doesn't necessarily imply that they're Ghibli-like, though ...):
- Fullmetal Alchemist
- Fairy Tail
- D.Gray-Man
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Or else, if you liked the "Eastern" (High) Fantasy Setting with wolves and spirits of e.g. Princess Mononoke, maybe this one will be good for you:
- InuYasha
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Or if you like magical girls ( "witches") who can fly (e.g. Kiki), maybe this one:
- Cardcaptor Sakura
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Because Ghibli has so many different movies , depending on which ones you liked, there's a lot of different manga which might be good for you.