For myself, I really like doing the whole weights thing. As has been mentioned, though, you want to use multiple muscle groups together and avoid machines if you want to get real strength. The only machines I ever use are things coming off of a pulley; most exercises I do are either body weight, dumbell or barbell.
One piece of equipment that I suggest that you get is a swiss ball. There are a lot of exercises that you can do with one that work things differently than just laying on the floor. If you are sitting or laying on one, you can do most exercises such as crunches or
bridges or
bridges with a knee tuck on them. This will work not only the muscles targetted by the exercise, but also your stabilising and support muscles that have to keep you from rolling around.
Other good exercises could be supine hip extensions and leg raises with a swiss ball grasped between your knees.