Keith Norris http://theorytopractice.wordpress.com/ writes a blog I like that has some great ideas for short intense workouts. I never have trouble sleeping after a heavy deadlift session, for example, and you can annihilate yourself in 20 minutes of lifting. Alternatively you can mix stuff throughout the day: pushups, pullups, etc.
Love it! Think that's just what I need, as it takes me around 20 minutes to walk each way to the gym, so I want to be as efficient as I can whilst I'm there.
There's also some stuff I could do from home the days I don't go to the gym by the sounds of it. Thanks!