Some good alternatives to not going to the gym are buying a bowflex or some other piece of machinery. I personally enjoy going to the gym everyday. It not only helps maintain your body but helps relieve stress, plus for me its something ONLY for me.
People say they never have enough time for themselves, so being at the gym is my time for myself. Just something to think about.
However, I also agree with everyone here. You don't necessarily need a gym. I only own one piece of exercise equipment, a pull up bar at my house. I do push ups, sit-ups, crunches, leg lifts, and yoga, P90x, and run around my neighborhood(on the days I don't go to the gym).
Also, picking a gym is hard. You have to find somewhere your comfortable, if the place doesn't feel right when you try it out, go onto the next one. Also, If your not a morning person I would suggest finding (if you do get a membership somewhere) a place that is near/on the way to and from work, that way you can stop and workout before going home instead of finding an excuse not to go.
(ex. too far away, i'll just go home for a little bit after work, etc.)
Just some things to consider.