You should check out this awesome fitness app that I just started using. It's a great app that trains you to do pushups and allows you to complete different challenges and try to beat your scores. You can even challenge Facebook friends to pushup challenges. It's pretty awesome. The website even says that they will be adding other exercises soon.
Website: Drop and Give Me - Fitness Anywhere
Market Page: https://market.android.com/details?i....dropandgiveme