You should try cycling. Not spinning away at the gym staring at a wall but getting on a bike and going out for a nice ride. It is a lot easier on the knees than running and its a lot more fun. If you live near some trails you could even give mountain biking a try. Thats great for cardio and general fitness.
For overall fitness, hard to beat running, even though it can be hard on the knees. Swimming and biking run close seconds. But if you're trying to lose weight, it doesn't make much difference. Whatever gets your heartrate up will work.
Do alot of things with very little rest time in between each excercise. 1 minute run, then 1 minute pushups, then 1 minute run, then 1 minute crunches, then 1 minute run, then 1 minute pullups, then 1 minute run, then one minute jumping jacks, then one minute run, then one minute leg lifts, then one minute run, then one minute whatever and continue doing this until you get all the excercise varietys you want, then repeat.
With as little time in between each excercise as possible. That will really poop you out, but once you get used to it, your overall fitness will go through the roof
gymtime is right...in my opinion. There are no wrong answers when it comes to exercising. You might want to think about incorporating interval training (high intensity bouts followed by low intensity bouts) that is the most intense and calorie burning way to exercise. I would do it on a tredmill, because more muscle groups are involved, also it just feels like the best way to overload the cardiovascular system....actually basketball i think is the best(because it is fun also).