I cant have a favorite, just ones i really fucking liked.
SAC was fucking awesome. Planetes too, though at a slower pace in areas. Right now i have a shit of stuff to watch such as Trigun, Noein, Geneshaft and black lagoon.
the animation in some of the first ep of noein is fucking amazing, i hope they continue the trend.
I also like more abstract work like Mononoke and mushishi where it was more about making a beautiful anime (mononoke for visuals, mushishi for concepts).
I really liked claymore too.