Most Visually Stunning Anime...

Dragon Ball Z - Very good scenarios. Repetitive scenario however. Good for the competition between (San)Goku and Vegeta.

Saint Seiya - Very well drawn and marvelous musics. Good moves too. My favorite !

Goldorak - a beautiful scenario but just a good memory of my childhood.

Astro Boy - Just the good memory of my childhood.

One Piece - great scenario, even if repetitive like Dragon Ball Z and GT. I love the moves in the fights !

City Hunter [Nicky Larson] - I like the humor. And a lot of details on the guns, rifles, etc .... are well respected.

Ken the survivor - Very well drawn, better than Saint Seiya in the picture, but very bloody scenario. A souvenir of my childhood.

The Big O - Of course, I have just the Big O DVDs. I fell in love for this anime, that's all. Even if it has faults like the pictures, and the scenario. But moves are well done.

My top four would have to be:

Millennium Actress: One of the best movies you will ever see, and the whole concept is amazing and stunning.

X (The Movie/The Series): Whether or not you look at the movie or the series, X is one of the prettiest anime out there. While the dub of the series make me want to cringe, the character designs are really drawn and the crispness of it is refreshing. The ruins of Tokyo never looked better.

Le Potrait de Petite Cossette: One of the trippiest, weirdest animes I've ever had the pleasure of seeing. But it's gorgeous, so I don't have to get it.

Saikano: The way this series is animated is what makes it visually stunning. The cute character designs (i.e. the constant blush) make the dark story pop.

And a couple of "just cuz they are"s:

Metropolis
Howl's Moving Castle
Red Garden
Escaflowne: The Movie
Hitsuji no Uta

Lady Oscar !
Les mondes engloutis
Les Schtroumpfs (The Smurfs)

Despiting the Big O (they bought me with Megadeuses design...), most stunning (visually) animes would be (there is some of them ):
- Fullmetal Alchemist
- Ninja Scroll
- Vampire Hunter D II: Bloodlust
- Neon Genesis Evangelion