Vectorizer.io - Fast and easy way to vectorize an image online
Bulk Resize Photos - Resize large photos in bulk
potrace - Open source program that transforms bitmaps into vector graphics.
ResizePixel - Free image editor to crop, resize, flip, rotate and convert images online
Autotracer.org - Free online image vectorizer
Dribbble Resizer - Resize your designs for sharing on Dribbble