For pure 2D pixel art, i'd say Aseprite for the win. With v.9.1 out, so much has been added and improved.

Its open source, no catch. Constantly being updated and improved. It has: Layers support Proper alpha channel unlike GraphicsGale.. meh!, Has onion skinning. Color palette ramp. Simple and much cleaner UI. Unlimited undo options. Mini editor. Import/export sprite sheets option. Split view for more freedom and so on, and none of the "overrated" and "out of this world" stuffs you would get from this blah and this bleh.

Simple and yet reliable in every way.