All of the following resources are interactive and great for teaching online or on an interactive whiteboard. Spending a little time exploring the options allows them to be used to their full potential.

www.topmarks.co.uk/learning-to-count/paint-the-squares - clear and simple to use.
www.ictgames.com/mobilePage/hundredSq - twist the dial to show numbers greater than 100 or less than zero.
www.mathsbot.com/manipulatives/hundredSquare - show as base 10 images and show numbers greater than 100 or less than zero. www.mathsframe.co.uk/en/resources/resource/71/itp-number-grid - hide numbers under a shape, alter the number of columns and explore multiples