Movies like Toki o Kakeru Shoujo and short series like Byousoku 5 cm would do. Simple, nice and easy.
If they're hooked i recommend that you give 'em:
Blood+ if they like action
Honey & Clover if they like romance
Ouran High School Host Club if they like humour
Bartender if they like delicate stories
Beck/Nodame Cantabile if they like music-themed ones
FLCL if they like funky jazzy stuffs
From there we can continue with the "heavier" ones.....Slowly pulling them into the unescapeable black hole that is anime and manga......
Ecchi stuffs, otaku-knowledge-heavy ones and "scary" bunches like Tenjou Tenge, Lucky Star, Sekirei, Yu-gi-oh, Welcome to the NHK and others like those would just scare the new audiences away.