Exercise Every Day

This! There's an emerging consensus that crunches are kind of crappy for doing anything except stressing your back (spines not being designed to be exposed to shearing forces while flexed like that); it's much more useful to do things like planks that work your muscles' ability to stabilize your spine in a "neutral" position.

And Stumptuous is full of good stuff. There's an article on push-ups (and how to get to one) which might be especially relevant to your interests:

http://www.stumptuous.com/mistressing-the-pushup

Also, lifting_heavy_things, which has had some fun posts on "stuff you can do with no equipment for no money".