This site has printable pdfs with lots of activities that involve minimal prep and equipment. These activities are matched with grade-level curricular content.
Active academics has a bank of activities available for grades pre-K through 8 and a search tool for specific curriculum content areas. It does require you to create a free account online.
ABC for Fitness
Clicking on the image will take you directly to the teacher resource manual. There are activities for grade K-5, with classroom content worked into the activities.
American Heart Association
These are ideas for classroom activities. There is not much "how-to" but this site provides a lot of inspiration for the value of quick breaks from teaching content.
Let's Move West Virginia
This is a large resource guide for classroom physical activity - scroll to the middle for active lessons and activity breaks.
5210 Let's Go
This site has a set of printable cards that you can put on a binder ring, created by a school in Maine. Most of the activities are not integrated with curricular concepts.
Go Noodle is a web resource with 100+ videos. Many videos offer physically active lessons, although some are just activity breaks. It does require you to create a free account online.
This site provides 54 separate videos of activity leaders alongside students performing the activities, with music. Whereas Go Noodle is animated, these videos have more of a "home video" feel and have actual students demonstrating the activities.
Just Dance Kids
Just Dance is a video game for kids, where they follow the dance that the avatar is doing. Some videos are available on YouTube with a search of "just dance kids" - see if your class has requests!
Cosmic Kids Yoga
These are videos for yoga, meant to provide relaxation. Choose between longer story videos or brief guided relaxation videos.