Faves:
(no real order)

Shaman King (great concept and characters)
Yu-Gi-Oh (I think the concept is what made it, a card game to save the world makes as valid a fantasy world as giant robots etc)
Ikki Tousen (Oh yes, the fan service of it all)
Cowboy Bebop (A classic, if you don't like it you're just wierd lol)
Full Metal Alchemist (Very well drawn and has it's moments where you have to think about stuff)
Escaflowne (I like the imagry in this one, plus archaic mechs was pretty cool)
Outlaw Star (Just a fun trip with good music and characters)
G Gundam (best concept for Gundams ever, good art for it's time and some nice tense episodes)
Vampire Hunter D: Bloodlust (A gem of anime, if you haven't watched it yet go do so)
Hayao Miyazaki, or anything done by him (He's a national treasure, seriously a genius)

Least:
Bo bo bo...bo...bo...however many "Bo"s there are
One Piece (the American ANIME) (the manga is really good imo)
Naruto (American ANIME) (See One Piece)
Inuyasha (Quite possibly the worst anime I have ever seen)
X (I'm all for the gothic thing and all, and the movie was good but man, the show was just too much for me)