At the boxing gym, there was a chin-up bar across the top of a doorway, and I surprised myself by doing three quick chins on it. I've always wanted to be able to do a chin-up. Back in high school, during the President's Physical Fitness test, I was humiliated (a common occurrence in gym class) by not even being able to hold myself above the bar for one second. When my daughter was little and frequented playgrounds, I worked my way up to holding myself above a monkey or parallel bar for a few seconds, but came nowhere near being able to pull myself up. Now I can. Ha ha.
Now, I love the big iron, but you don't really need weights to do some major strength conditioning. Unlike a lot of weight training, which isolates muscles, bodyweight exercises work a wide variety of muscles at one go. Chin-ups and pull-ups strengthen your chest, shoulders, biceps, and lats--and that's a lot of bang for your buck.
Other bodyweight exercises I like to do while waiting to go back to the gym include classics like push-ups (I can do 25 regular ones--I was doing 50 on my knees, until I read some trainer saying "girl" push-ups were useless). Try all the styles: triceps push-ups, diamond push-ups, fingertip push-ups, and when you can do loads of regular push-ups, the dreaded one-handed push-up (I'm not even close).
There are also a metric ton of different crunches and sit-ups you can to work different parts of your core. At kettlebell class on Saturday, we learned the Janda sit-up, which is tricky to execute properly, but is supposed to rip you a new set of abs. We'll see.
If you're interested in a full-body bodyweight exercise, look into burpees, in which you basically fling yourself from squat position to push-up position, back to squat, and up into a jump. They develop explosive power and get your heart rate soaring if you're into that kind of thing. I'm also fond of bodyweight exercises using equipment at the gym, like the hyperextension and, especially the triceps dip, which, only a few short months ago, I couldn't do at all, but now I can do up to 6 reps at a time on. Sweet progress.