Stay away from the pec fly machine. Them things is dangerous. In any case, it's probably too soon after surgery to start working out your upper body. Check with your surgeon, but my plan is to wait at least 6 to 8 weeks before I do any weight work. Once you get to that point, you can do a lot just with body weight exercises -- there are all sorts of variations on pushups that work different parts of your chest. If you can't manage regular pushups, you can start by doing them on stairs -- start where it's comfortable, and gradually go a step lower as your strength increases.
I'm a fan of free weights, and I'd probably start with dumbbell presses on the floor. You get more "bang for the buck" with a given amount of weight with dumbbells, and if you're on the floor, it limits how much you can lower your elbows, which will help to keep you from stretching the skin of your chest (and your scars) too much.
Also, check out the difference between bodybuilding routines and strength routines at some point. The general wisdom is that to build muscle size you should be doing more reps and more sets at lower weights than you would just to build strength quickly. And diet is important, of course. Lots of resources out there on the web, but be conservative -- aim for a high-protein diet without resorting to supplements -- some of them can be really bad for you.
