I found the Insanity workout series very good when I was trying to improve my fitness. It's mainly bodyweight cardio exercises and will drastically improve your fitness, but it's also definitely not for everyone. I found having a focus and instructor motivational, while my wife found it boring and eventually monotonous. She greatly prefers to take group classes at the gym. Probably the best thing to do is find a hobby that is also physical activity, enjoyment is a hugely important part of maintaining motivation. What you will probably find though is that once you have been exercising for a few weeks, you start to gain motivation from your own improvements, further reinforcing your motivation. It's that first three weeks of so that are the only real struggle.