Rubber mats will protect the concrete floor of your garage pretty well, just don't abuse them.
Also, get free weights and a Physio-ball. You can substitute all bench exercises (incline, decline, flat, and military) with the ball and work your core, at the same time. Alternate arms on the press, while keeping both pressed up in the air. So, both are straight up, bring left down to the chest and up, then do the right down to the chest and up. It is much healthier for your body that way, and if you don't have a spotter and your arms give out, you have a less risk of the weights landing on your chest and causing serious damage. You can then flip over and get your upper back workout in. Butterflys, as well as the headbanger motion exercise, I'm not sure the real name for it, but Beavis and Butthead do it.
It's real good for your shoulders. You don't need heavy weight.
I am not a fan of the straight bar, if you want to do close chained exercises do pushups.
Do abs, lower back, hip flexors, and hammies on the Physio-ball, and/or your mat floor.
Do leg exercises with the free weights. Squats, lunges (single leg with back foot on the Physio-ball). Lay on your back, with both heels on the Physio-ball, and pick up your body so you are resting with your shoulders on the floor and feet on the ball, lift one leg, and roll the ball in towards your butt, then back down and switch.
Those are just a few exercises you can do. I firmly believe you can get not only an in-shape looking body, but also an in-shape athletically body, with nothing more than a Physio-ball, some free weights, and your own body weight. If you want to incorporate your abs throughout the day, use a Physio-ball as a computer chair. It get very easy very fast, and you are basically getting a minor ab workout the whole time you play on the computer.
I have bazillions more exercises, if you need any more. Make sure you get cardio in as well. Do not try to lose belly fat by doing situps. You will just end up with strong muscles under a bunch of fat. Noone will ever see them.
Good luck!
P.S. I knew an Olympic javelin thrower girl, that could do squats on a Physio-ball. She had some crazy abs too. I have never seen anyone else that could do it. I know a lot that claim it and fail when they tried, but she did them in her workout.