Another pose you can always rest in during class is your Downward Dog; this pose is central to many traditional vinyasa sequences (series of poses linked together with inhales and exhales), like the Sun Salutation, and also provides a nice stretch on its own.
Start on your hands and knees on the mat, with your toes tucked under. Spread your palms wide, about shoulder width apart and slightly in front of your shoulders. With a exhale, lift your knees off the floor and think about moving your hips up and back while you straighten your arms and legs and push your heels into the ground. Push out of the ground evenly with both hands and feet, firming up your arms and legs without locking your knees. Keep your head between your shoulder blades, without letting it hang and straining the neck.