- The Hundred: Lie on your back with your legs up in the air at a 90 degree angle. Lift your head and upper body and begin pumping your arms up and down. Inhale for 5 and exhale for 5, making sure to push your abs towards your back while you exhale. Count up to 100. You can increase the difficulty by lowering your legs to a 45 degree angle and/or going for longer than 100.
- Criss-cross: Lie on your back with your knees bent. Place your hands behind your head and lift your head and upper body and bring it towards your opposite knee. Alternate sides. Begin with a set of 10 and work up to doing 30-50.
- The Plank: This one kills but works the best! Face down, bend your elbows and lift your body (legs extended behind you). Make sure to stay perpendicular to the floor, holding yourself up with your abs. Hold for 30 seconds. Stretch by extending your arms and tilting your head back. Do two more sets of 30 seconds, making sure to stretch in between each. Work up until you can hold this position for 1 minute and do 2-3 sets. Another variation of this is to drop your knee to the floor while you are in the plank position. For more of a description and other variations, check out Runner's World.
Enjoy! :)