If you don't have a jointer or a planer or you need to flatten something large or difficult to flatten, building a simple sled for your router is a great solution.
The router bit I am using: http://amzn.to/1tswZzd [Affiliate link]
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A Day in the Woods: http://youtu.be/ee-rt2FDf5Q
Integral Beaded Door: http://youtu.be/2TJVNEMmjGg