Symbaloo
Symbaloo is a website that lets you create buttons that link to websites. You can add images to buttons so it is easy for kids to recognize. This is useful for keeping kids on webistes that you want them to go to and to help them easily navigate around the inter-webs independently.
If you are studying modern art, you can create a "webmix" of sites where they can learn about modern art etc. You can make a webmix of origami videos, linear-perspective videos or cardboard sculpting videos.
I use computers as a center and have a webmix of several kid-friendly makerspaces the kids can chose from.
Another thing Symbaloo is good for is writing this blog post. Here is a webmix of all the sites mentioned here:
Ten Websites for Art Class
Pixlr
My school district just made PhotoShop available to elementary kids this year. But, before that Pixlr was a super helpful, free, web-based Photoshop-like app. It is greal for teaching kids the basics of computer -based graphics When they get to high-school digital design and yearbook classes they will be more familiar with the content. I used this program with 4th and 5th graders.
Chrome Build
This site is just so nifty, and the kids LOVE it. It basically lets you build with LEGO digitally! I am not sure what the educational value would be beyond what building with regular LEGO is, but it is just so fun. I think it gives kids a greater spacial awareness :). It also lets kids publish their creations on a Google Map. They can build your town a new stadium, or themselves a new house. It is the best.
Virtual Instructor
This site has lots of practical drawing and painting skills. There are videos for blind contour drawing, perspective, shading and much more. They are great for higher ability kids to explore independently, for guest teachers to show, or for you to show if you, ya know, don't feel like teaching for a minute.
ABCYA Animate
This is a super easy animation program. I have let kids as young as kindergarten use it, but it is still engaging for kids up to 3rd and 4th grade. I think this is a great program to use if you plan on doing claymation videos or some other form of manual animation. It gives the kids a better understanding of what they are doing. It can also be used as a planning tool.
Origami Player
A huge directory of easy step-by-step origami videos kids can follow independently.
Google Art Project
Can't take your kids to the Louvre? Take them on a virtual tour. I have my second graders build an art museum each year to learn about architecture, art museum careers and differences between art genres. This is great tool to give them some background knowledge. It would also be great to use to prepare students for a trip to the local art museum.
Incredibox
This is a music making website that lets kids compose songs. I have used it to let kids make background music for videos they have created. It would be great to use it in collaboration with the music teacher so maybe s/he could actually give the kids some composition tips :).
PicassoHead
This site lets kids make a Pablo Picasso inspired head. It is super easy to use, so it is great for kindergartners to get a taste of graphic design and to use as an extension/ early finisher activity for a cubism lesson.
HelloKids Drawing
This website is a more kids friendly version of the virtual instructor above. Lots of drawing tips and how-to videos. The draw back of this site is that is lots of link elsewhere, so you have to keep a close watch to make sure your kids don't end up on the other side of the web.