#1 Extended Child's pose (or puppy pose) and #2 Child's pose. A favorite of mine for a tight low back, tension headache, or overall calming. Take 5 minutes here, experiment with your arms above the head or back by the heels. You can even walk the hands to the right of your mat or the left. Breathing deeply, closing the eyes, massaging your forehead into the ground (or a blanket, block, bloster or pillow). If you are pregnant you can still do this pose, just spread your knees wide and leave room for baby belly.
Here is a great link to walk you through the pose and point out its benefits for the body. Enjoy!