For those with Amazon App Store access you can grab this 5 Star App for free. Simple, fun, and challenging:
http://www.amazon.com/gp/product/B00...8&ref=mas_faad
For those who don't have Amazon access you can get it at Slideme for a mere 99 cents. Well worth the price in my opinion. Slideme accepts Paypal.
http://slideme.org/application/quell