I'm probably in for a slapping but...
Fist of the North Star/Hokuto no Ken characters. Oh, the manliness shrunken down and converted into superdeformed plushiness!
I'd love to see Kenshiro in multiple versions along with Bart/Bat, Lynn, Lui, Rei, Ryuga, Juza, Ein, Falco, Kaioh, Hyoh, and Shachi. (And possibly Yuda/Juda and Jagi just for the lol factor.)
And City Hunter plush! Ryo Saeba and Kaori. Heck, even Umibozu would look ridiculously fun.