Great website developed by Sue Looney. There is something here for everyone! Engaging math problems that can be done as ten-minute math, or to launch your core lesson, or to share during morning meeting. The more I investigate this site, the more I like it. Everyone can access the problems and they strengthen students ability to make comparisons and think deeply. Click on the picture and it will take you to the whole site.
This is the link to Graham Fletcher's website. He's kind of rockstar in the land of twitter. He makes short "3-act" videos for elementary school teachers and students to learn from. They are fun and thoroughly engaging. He links each video to a specific Common Core content standard.
Here's another site I love. It's created by a middle school math teacher who focuses on visual mathematics. The problems she shares are definitely for middle schoolers but I think you can use the visual pattern problems with almost any age. See what you think!