potrace - Open source program that transforms bitmaps into vector graphics.
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!
Karbon - Karbon is the scalable vector drawing application in KDE.
Autotracer.org - Free online image vectorizer
Adobe Illustrator - Adobe Illustrator is a vector graphics editor.
Vectorizer.io - Fast and easy way to vectorize an image online