Paripurna Navasana, aka Boat Pose
How to do it: From seated, lift the legs and balance on the sit bones (the bones beneath the fleshy part of your bum), engage the core to support the lower back, and draw your heart towards the thighs to keep the spine long and straight. Fan your toes and engage your inner thighs. If you have back problems, or are new to yoga, modify the pose by placing your palms under your knees and keeping your legs slightly bent, with your shins parallel to floor.
Makara Adho Mukha Svanasana, aka forearm plank
How to do it: Lie flat on your stomach, and place your elbows underneath your shoulders with your forearms flat on the mat. Spread your fingers and really push through those knuckles! Engage your core muscles as you start to lift the belly and thighs off the mat. Keep the tops of the toes grounded, and engage your inner thighs and lower abdominals. To work even harder, take your gaze towards your navel. To modify, untuck the toes, and gaze between the forearms.
Garudasana sit-ups (Eagle arms sit-ups)
How to do it: Lying on your back, take your heels up to the ceiling, hook your right thigh on top of the left, and your right ankle behind the left calf. Take your right arm underneath the left and hook at the elbow. Take palms to touch. Extend heels and palms away from one another, and on an exhale draw your knees and elbows together over the midline of the body, then inhale to extend, and exhale to draw together again Repeat five-10 times, then cross your arms and legs the opposite way and repeat another five-10 times.