Inkscape is a free SVG editor that provides good support for designing and editing SVG documents. Other design tools (Adobe Illustrator, Corel Draw etc) can be used to generate vector graphics and export them to SVG, but Inkscape, like SVG-Editor, has SVG as its native format.
It has good support for most of SVG's primitive elements and their attributes with tools for making Bezier curves easy to generate etc.
A useful feature is the import and conversion of images to SVG.
It has no support for generating or editing SVG declarative animation.