By digital camera standards, the three-year-old A420 is ancient. As fine as it was in its time, we'd advise against a purchase (if you can even find it). Here's what we had to say about it when it was a current product:
Canon's A420 (along with the 430 and 530) aims for the novice crowd with a simple point-and-shoot philosophy. The A420 is a 4 megapixel camera for entry-level users and aside from the ease of use, there's not a lot to go crazy over. The sensor is pretty small for today's standards, and the body, while sleek, isn't as flashy as Canon's exciting SD line. Even for novice or casual users, the A420 is a camera you'll probably outgrow fairly quickly, and soon enough you'll be itching to take those training wheels off and graduate to a better model. Skip the middleman and choose a camera you can grow with. This model might be a good choice for children or those with a passing interest in photography.