What kind of exercise do you like? And what is your goal -- building endurance, burning calories, getting stronger, all of the above?
There are a variety of exercise tapes available that you can do inside. If we know your likes/dislikes, it will help in making any specific recommendations. Walking/jogging outside is a good activity but somewhat weather-dependent.
And another thought -- increasing your weekend activity will help, but there may also be ways to increase your week-day activity too. It may not be a "work out" per se, but there are things you might do to weave exercise into your daily routine. Like taking stairs instead of the elevator, going for a brisk 15 minute walk at lunch time, stretching at your desk, walking to the next closest bus stop in the morning, etc. Do some sit ups and push ups during commercials when watching TV in the evening. All of that helps ... and it counts.
Just a few thoughts .....