Naruto. I love the messages of loyalty and perseverance.
That's a very tough one, but I'd have to go with either InuYasha, (because it's one of the first anime shows that I ever watched,) Angel Beats, (which is the first I saw of Key's many fine works,) or most probably the first anime I ever watched, Yu-gi-oh, season 0.
That's a tough one because I usually read the manga versions of everything. Hmm...I guess Gundam Wing! Hiro Yuui, you're still bad@$$ to me! >:D
Hellsing because big guns, big action, blood and the moral message...not to mention the soundtrack.
The Melancholy of Haruhi Suzumiya, because it has a nostalgic high school essence that fills the void of my high school experience, because I strongly identify with Kyon for some reason, and because I adore Yuki Nagato and the way she develops into an individual.
pokemon counts as anime, right?
then i say pokemon ^_^
Robotech. Because I grew up with it...
Film: Howl's Moving Castle (in Japanese, I don't watch Japanese anime in English, it takes away from the emotions and meaning so I watch with subtitles.)
In terms of series not that I've watched many it has to be Bunny Drop. That's better than Howl's Moving castle, the story is so beautiful and I love the characters, especially Daikichi and the little girl.
I'm not into anime actually, I simply don't 'get' them most of the time (they're so bizarre sometimes!), but I did watch quite a few because I seem to get along with japanophillic people very well. :-p
So I have to say: Ghost in the Shell, just because I think the concept is really cool.