Autotracer.org - Free online image vectorizer
Rasterbator - Wall art from any image
potrace - Open source program that transforms bitmaps into vector graphics.
Posteriza - Use POSTERIZA to design your own big posters and signs from any digital photo with your home...
Vectorizer.io - Fast and easy way to vectorize an image online
Block Posters - A free poster maker to create massive wall posters from your own images! Free!