I personally use GIMP and synfig (synfigstudio)
synfig is much better for 'real' animation, but it isn't exactly a polished piece of software. (and then I use GIMP to stitch the rendered PNG frames into a single animation, since synfig's GIF output was terrible last time I tried).
www.synfig.org/Main_Page
( ,
Fri 5 Jun 2009, 18:05,
archived)
www.synfig.org/Main_Page