Planks

These are just fabulous for your core and I think should be a part of every one's fitness repertoire. I use a lot of planks in classes and with clients because they work wonderfully. Yay, abs!
A plank is like the top of a push up, except that your hands are lined up underneath your shoulders. Maintain a straight line from heals to head; no butts in the air.
If you'd like to modify, prop your self on your elbows and forearms instead.
Now for the fun part; hold it. You may feel your sides start to shake, don't panic, just say hello to your obliques!
Remember to breathe, and aim for holding the pose for one minute. (Building up to it will probably take some time). Do it three times a week, on non-consecutive days.
These are great for beginners and experienced exercisers alike, and there are so many ways to use them. Watch for more!