potrace - Open source program that transforms bitmaps into vector graphics.
Splashroad Separation Studio - Quick and Easy Color/Shape Separation
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!
ZebraTRACE - ZebraTrace is a simple tool to trace bitmap images into a pattern of curves with a variable width.
Autotracer.org - Free online image vectorizer
Vectoraster - Generate custom vector halftones, line rasters and gradients