There is no need to join a gym or spend money buying equipment.

Try these ideas:
http://en.wikipedia.org/wiki/Category:Bodyweight_exercise

burpees are great for conditioning:
http://www.bodybuilding.com/fun/rossboxing2.htm

http://www.youtube.com/watch?v=c_Dq_NCzj8M

a few of the gorilla strength exercise videos:
http://www.metacafe.com/watch/833819/amazing_new_workout_1/
http://www.metacafe.com/watch/834006/amazing_animal_workout_6_gain_gorilla_strength/
http://www.metacafe.com/watch/834078/amazing_animal_workout_10_gain_gorilla_strength/


I do 2 or 3 burpees every once in awhile, about 10 sec. of panther crawl workout_6_gain_gorilla_strength and finish up with a deep squat into a chair.
Whew!