Strictly off the top of my head...
1) Ub Iwerks. Iwerks did virtually all of the animation for the first few Mickey Mouse cartoons. Known for his speed.
2) Norm Ferguson. Created, arguably, the first instance of true character animation in a short called "Playful Pluto". Pluto sits in flypaper and is shown to be thinking as he attempts to remove it.
3) Fred Moore. Known for the incredibly appealing quality of his drawings. Worked on the dwarfs in Show White and redesigned Mickey Mouse (changing the character from the white face/black eyes era into the Mickey we all know today).
4)Bill Tytla. Known for the volume and power of his characters. Perhaps his most famous creation is the devil from Fantasia.
5) Frank Thomas. The thinking man's animator. Known for his thoughtful and meticulous approach. Did Captain Hook in Peter Pan.
6) Milt Kahl. One of the best draftsmen ever to work in animation. He did Shere Khan (the tiger) in the Jungle Book.
7) Ken Harris. Chuck Jones' number one animator. Worked on numerous Bugs Bunny and Road Runner cartoons.
8) Rod Scribner. Bob Clampett's primary animator. Again, responsible for some terrific Bugs Bunny work. His animation has a rubbery, cartoonish quality that's often missing in other animators' work.
9) Glen Keane. Unlike everyone else on this list, Keane is still alive and working. He did Ariel in the Little Mermaid and the beast in Beauty and the Beast.
10) Marc Davis. If Milt Kahl has competition for the best draftsman in animation, Davis is it. He did Maleficent in Sleeping Beauty and Cruella De Vil in 101 Dalmatians.