This variation on Utthan Pristhasana (Lizard Pose) is one of my favorite postures for addressing tension in the quadriceps and hip flexors. The mild rotation of the spine opens the chest and brings the stretch high up into the psoas.
To enter the posture, come to a long, low lunge with the right foot forward. Drop the left knee, turn the right foot out at a 30 degree angle, and plant the left hand. Then bend the left knee and grasp the left foot with the right hand. Roll the right shoulder back and turn the gaze up toward the sky as you rotate the spine. Stay for 5-10 breaths and repeat with the left foot forward.