Reverse Crunches are great for abs!
Here’s the ab exercise I do two times per day. Trying to describe them to friends is difficult, especially just by description.
Here it is:

From Erin Kurdyla at Self magazine:
The Move-Reverse Crunch
Lie down on your back, hands at your sides. Bring legs into your chest, knees bent 90 degrees. Squeeze a ball (towel) between your knees. Then contract abs to curl your hips off the floor, and slowly lower down to start. Repeat for 3 sets of 12.
Tip: Breathe!!!! During ab work it’s easy to forget about your breathing, but it’s important and makes the movements safer and easier. Remember to contract and exhale, release and inhale.
Great lists from Exercise at About.com.
First, figure out how much time you spend doing the following:
Sitting at a desk
Sitting in a car
Sitting in front of a TV
Sitting in front of a computer
Eating out at restaurants
Drinking alcohol
Eating fast food or junk foods
Staying up late/not getting enough sleep
Now, how much time do you spend:
Being active in general (taking the stairs, walking instead of driving, gardening, cleaning, etc.)
Doing cardio exercise
Strength training for all muscle groups with challenging weights
Preparing your own meals and snacks and eating fruits, veggies and whole grains
Reading food labels
Tracking your calories
Sleeping
Dealing with stress in a healthy way
If you spend more time doing the things in the first list than the second, it’s time to reevaluate your priorities and decide what you really want for yourself. Living healthy means spending time and energy on your body–moving it around and paying attention to what you put into it. Staying in an unhealthy lifestyle means you can avoid expending energy, time and effort…but at what cost?