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!
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
Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
Autotracer.org - Free online image vectorizer