You have options. Your choice of media will be determined by several factors. 
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Yep, books are making a comeback.  A more practical interview with Terry Lents with ideas for using books will come soon.
Rather than whistle while you work, listen while you work. Have some quality content (audio or video) running in the background while you are handling your routine tasks. Your subconscious mind will absorb more of it than you think.
The more sophisticated e-Learning systems capitalize on the psychology behind multimedia training. The impact of this science is pretty amazing. Madison Avenue is using this technology on you with almost every TV commercial to entice you to buy. Now, e-Learning uses it to encourage you to grow.