The glute bridge is a great alternative to lower body exercises and can be used as an activation exercise before compound lower body exercises.  Squeeze your hamstrings and glutes to raise your hips off the ground, then hold on top for a short count, and lower back to the ground.  By changing where you press through the foot (either heel or toe) you are able to focus on what part of the leg you are working on.  A single leg variation increases the difficulty level for those looking for a better challenge.  By adding a band your goal is to now keep tension on the band and work the medial glute a little more.