I think Cowboy Bebop had me drawn in completely, together with it's beautiful production (direction, script, character etc.).
Wolf's Rain was excellent and has some of the saddest and cruelest moments I've ever seen in an anime.
For all out fun, FLCL does it for me. The creativity is amazing especially the choreography of the battles in it.
Since there are some Miyazaki fans here, I like Kurenai Buta (Porco Rosso) the most out of all his films.