Enter a grade level to narrow your results, if desired. I left that blank, but I selected Common Core State Standards, and then the Number and Operations in Base Ten 'sublevel'.
I was delivered a very extensive list, many of which are web-based practice sites to reinforce the core standard being learned. What was very cool: when clicking on 'Educational Standards,' ALL the standards that the website supports are delivered. Nifty.
Click 'Learn more about this resource' and you'll see a full page detailing the resource. The green box (lower left below) indicates the Education level, what type of resource (e.g., instructional material, reference) and the subjects included.
CC Connection: I think this will be an extremely valuable source linking the teacher to common-core referenced 'tools'. Math teachers - check out this resource when you get time. Be prepared to get sucked in; I suspect time will fly by as you find useful tools to use!