Vectorizer.io - Fast and easy way to vectorize an image online
PNG to SVG Converter - PNG to SVG Converter is a dynamic platform that offers you to convert PNG images to scalable vector graphics without any difficulty.
Autotracer.org - Free online image vectorizer
vectorization.eu - Free online vectorization tool that can help you turn black&white and colored images into a vector format.
RasterVect - Professional raster to vector conversion program (vectorizer).
potrace - Open source program that transforms bitmaps into vector graphics.