I workout before work...I never thought I could do it, but now I get up at 4:45 a.m so I can get my workout in at the gym before going to work. It's a great way to start the day, and I never skip it because I'm too tired.
If I try to work out at the end of the day, it's way too easy for me to cheese out because I'm tired, grumpy, etc.
As for easy workouts...one of the best ways to get cardio is just to go for a walk, fast enough to get your HR up. After doing that for a while, you could start incorporating intervals of running.
As far as efficiency in burning calories, I think the elliptical is the most bang for your buck.

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Most wanted jeans: Green Rainbows! 26/27
Also looking for Paige petite Robertson 27 & Ellis Island Lexie 26 on the cheap