I think it was the mythology aspect of Princess Mononoke that appealed to me as well, that and the wonderful animation and the story. Porco Rosso is also a very good Ghibli movie. It is set in a slightly alternative world just after the First World War (or a similar war in that alternative world) and set in/around the Adriatic Sea. Like many of their films there are analogies in the movie, including why the main star is a pig, while everyone else is human. Howl's Moving Castle is also a nice movie. I personally preferred the book it was based off (a book of the same name by the late Diana Wynne Jones), but that could just be due to me reading it as a child before I saw the film. The film is still good, and sure as hell beats pretty much anything Disney spits out (the same could be said for everything Studio Ghibli does, their works really put the multi-billion dollar Disney to shame). A Nazi era rocket scientist? Do you mean The Wind Rises? While some of it does take part during the Second World War I think, it follows the main character from before then, through his life and his work developing aircraft before and during the war. I think it wsa incredibly popular in Japan, but not so much in the US due to the theme perhaps.
Have you seen Ghibli's Grave of the Fireflies? That is a very sad yet well told story set in Second World War Japan. Some of their earlier works are probably still among their best, due to the stories they told and how they told them.
After thinking about it since last night and my talk with the Bunny, I think my all time favourite is actually Nausicaä of the Valley of the Wind. It is not technically an official Ghibli film, as it was made before the studio was officially established, but it still is, and is the first of their films I saw, and I absolutely loved it and it is what got me into Ghibli movies. I even have the limited collectors edition hardback manga of it somewhere.
Overall I would say any Ghibli movie would be a good choice to watch. Some are of course better than others, but they mostly all have their strong points, quite often the stories, which being Japanese (although also based on Western stories) do tend to give us in the West a different play on things over the usual US crap we get recycled over and over again (such as copy and paste super hero movies and Disney and all the princess movies, for example).
