If you're a street artist, or at least a fan of street art, you should check out Spray Chalk. This awesome product allows you to graffiti the streets without risking fines or jail time. This brilliant art product is available on Amazon from Krylon.
It's completely temporary, so expressive buyers don't have to worry about messing anything up. This is a great non-commital solution for graffiti in the streets. Best of all, you'll be able to easily get rid of any less-than-brilliant attempts at street art simply with just a little soap and water.
It's a super fun product for kids, and would certainly add a new dimension of creativity for art projects outside the classroom.