SVGpage is an application that will render PNG images as SVG files or convert an SVG file to a PNG image. It uses an internal version of Autotrace. This is not a straight conversion to SVG (as there really is no such converter) but it does a fairly literal job with simple shapes, and renders a "painterly" effect for more photographic-style images.
OpenIcons is a set of SVG icons intended to be used on the Web. All the icons are vector-based and made using InkScape. The icons can easily be converted from SVG to pretty much any common graphics format. Since the icons are meant to be used primarily on the Web, the default distribution of the icons includes PNG copies of all icons scaled to the following sizes: 16x16, 32x32, 64x64, and 128x128 pixels.