potrace - Open source program that transforms bitmaps into vector graphics.
RasterVect - Professional raster to vector conversion program (vectorizer).
Vectorizer.io - Fast and easy way to vectorize an image online
vectorization.eu - Free online vectorization tool that can help you turn black&white and colored images into a vector format.
Vector Magic - Easily convert JPG, PNG, BMP, GIF bitmap images to SVG, EPS, PDF, AI, DXF vector images with real full-color tracing, online or using the desktop app!
LineTracer - Tool for converting scanned hand-drawn sketches to vector format