Aviary would have to be one of the most innovative software companies going around at them moment. They have created free versions of Garageband, Photoshop and Adobe Illustrator that are rich in features and run straight from the browser. Myna - Aviary's version of Garageband is still one the most impressive pieces of web programming I have ever seen and it really gives you an insight as to what can be achieved in the browser.
They have just released an educational suite including their image editor (Photoshop wannabe, vector editor (Illustrator wannabe), Audio Recorder (Garage band Equivalent) and music creator for students as part of a specific suite. The benefit students gain from accessing this over the traditional net is that all images as are kid friendly and you can access work they are doing.
Sign up for it here. Might be just what the creative / artistic teacher is seeking.