RasterVect - Professional raster to vector conversion program (vectorizer).
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.
LineTracer - Tool for converting scanned hand-drawn sketches to vector format
Vectorizer.io - Fast and easy way to vectorize an image online
potrace - Open source program that transforms bitmaps into vector graphics.