I downloaded a free app for my iPhone called 100 Push-ups. It's so simple its genius: the app trains you, over the course of 6 weeks, to do 100 push-ups. That's it.
I'm only in week one but I really love it and here's why: it's my ultimate fantasy of goal attainment. The app tells me what to do (whatever number of push-ups in a set, how long to rest in between sets) and if i just do what it tells me, I'll reach my goal. If only everything in life was like that!!
Here's the website which is chock full of info and will get you to the app (you can do the program off of the website, sans app, if you want).