Do you remember when you had to cut pictures from magazines and use your old postcards for images in the classroom? Now, of course, in two seconds Google images will provide you with more images than you can ever need. Even still, it is useful on occasion to dip into more specialised sites.
Here is a cheerful, easy to use clip art site: http://www.clipart.com/en/
Enchanted Learning provide a wonderful and easy to use picture dictionary http://www.enchantedlearning.com/Dictionary.html Apart from flashcards, this is great for use in class with IWBs or for setting homework and encouraging kids to use it outside of class.
Here is a simple site for personalising images http://www.imagechef.com/ Quick to use and adds fun and colour to any worksheet or IWB activity.
Want those images to move? There are many sites out there for creating comics and your own online mini films. One of the easiest to use is http://www.dvolver.com/live/home.html Good fun in class or again for homework and obviously the films created can be used to practise any grammar or vocabulary topic.