There are a number of ab exercises that can be done. But first and foremost...your diet must be good. After that, your physical activity.
I can't elaborate too much on this...as this post could end up being extremely long. However, directly answering your question...there are a few exercises you can do.
Click on this link.
http://www.thetrainingstationinc.com/ab-exercises.html
The first row (from left to right) is excellent for beginners. No equipment necessary. The second row is a bit more problematic w/ some people because of the use of machines. However, you can still do the Ball crunch.
Since it is still summer, all of the fitness magazines have ab routines right now. Pick up a copy and look at the exercises. This is especially true for the men's fitness magazines. In fact, for men and women,...I recommend picking up a copy of Muscle & Fitness. It is a great magazine. Lots of photos and descriptions. Very general overview on the "sport" of bodybuilding. Just don't let the word "bodybuilding" deter you from picking up a great magazine. It may be geared for the more serious individual, BUT the information in there is invaluable and it works. Sure we're not necessarily bodybuilders and that is not necessarily our intention, but the routines work.
Also, Muscle & Fitness has released a sistser publication (for women) called Muscle & Fitness HERS.
Here is a great company to purchase products from. My gym purchases from them and I will be placing an order w/ them shortly.
http://www.power-systems.com/Fitness...s/default.aspx (I made a link directly to the abdominal section for you).
Good luck. Send me a PM if you have any questions regarding diet, exercises, etc.