As some other artists around here may attest, MS Paint is quite capable of producing good avatars, though you also require another program such as GIMP or IrfanView to resize avatars. Paint.Net isn't strictly necessary (although it helps a lot! ).
For example, here is something I made yesterday in MS Paint (resized with IrfanView):
Spoiler: YellowCleric
Please rehost if you use it.