Hour of Code

Lots of options on Hour of Code.com

I recommend: 

First Grade- Kodable

Second Grade- Robot Islands

Third Grade- The Foos

Fourth Grade- Code.org - Minecraft Voyage Aquatic

Fifth Grade- Mario's Secret Adventure

Sixth Grade- Compute It

Other resources

BotLogic

Harry Potter (code.org)

The Grinch

Google Santa Tracker Codelab &

 Santa Tracker Code Boogie (Only available in December, best for primary grades.)

Lego- Bits and Bricks

Robot Islands 2

Pixel Hack

Scratch

Blockly

Code Combat

Code Monkey

Code Monster

REPL

CodeAcademy

Khan Academy

Google Grasshopper