The lack of response so far may be due to the fact that so many other "give me a workout" threads are both currently running and seem to be asked every week.
So if you go through a couple of pages, you can see responses to similar requests.
For an overview of the multiple goals in fitness for a tennis player, check out Sports Fitness Advisor Tennis Training Section:
http://www.sport-fitness-advisor.com/tennis-training.html
From the above, you'll see that the biggest ultimate goals will be to increase your speed and quickness on the court, increase your core strength to power your strokes, and work on your arms/upper body so as to avoid injury from a long season of ball bashing.
The Off Season Training Section
http://www.sport-fitness-advisor.com/off-season-training.html gives one workout regimen that should not be that hard to do.
If you are interested in using weights to increase your overall strength, you can begin with Complete, Annual Tennis Weight Training Program
http://www.sport-fitness-advisor.com/tennis-weight-training.html
Notice that rather than jumping into plyometric/power exercises, there is first emphasized a period of increasing overall muscle, tendon and ligament strength. This is not just to make your power training more powerful; the increase in strength will make you less likely to suffer injury doing plyometric work.
(I have to admit I think free weights provide advantages that machines do not, so that a three part program similar to the above, but using the following free weight exercises is better:
Tennis Weight Training - Exercises of Weight Training for Tennis
http://optimumtennis.net/tennis-weight-training.htm
Notice that Sports Fitness Advisor stresses doing a rotator cuff/arm program throughout all phases of exercise to help prevent the all-too-common overuse injuries that plague tennis players. I think the thrower's ten is the best of these workouts that can be done 3x/week throughout your training:
http://www.muhlenberg.edu/pdf/main/athletics/athletic_training/throwers10.pdf
It should be obvious after reading the above that you can't maximally train for strength, speed, endurance and power all at once. Going through the mutliple phases with a goal of peaking with speed and power at the end, with a firm foundation of leg, core and arm strength to prevent overuse injury, should be your goal.
Therefore as you get closer to the start of the season incorporate more of the following into your workouts:
Tennis Fitness - Medicine Ball Workout
http://www.youtube.com/watch?v=OV9boPlrlB4
High Intensity Interval Training (HIIT):
http://www.intervaltraining.net/hiit.html
USTA agility drills:
http://assets.usta.com/assets/1/USTA_Import/USTA/dps/doc_437_269.pdf
As many questions undoubtedly will arise, having the following book available for reference would be a great idea:
Tennis Training: Enhancing On-court Performance
http://www.amazon.com/Tennis-Traini...id=1348666463&sr=8-3&keywords=tennis+training
And for actual training blocks with very specific regimens, it is hard to beat Power Tennis Training
http://www.amazon.com/Power-Tennis-...d=1348666726&sr=8-24&keywords=tennis+training
Finally, I think many have benefited from the P90X training. It's great attraction is that there is a regimen that you don't have to think/plan - just do it and you likely will be fitter than when you started.
It's just that you won't have the same leg/core/arm strength as the above regimen, and won't develop the same power and speed/quickness.
But it takes real dedication to keep going.
Good luck!
