Having a cycling goal is very motivating if you're a goal-oriented person. It works well for me because I hate failing at something I set out to do. I went from very out of shape to quite fit and racing by setting progressive goals- half century, century, death ride, everest challenge stage race. Pick goals that are possible but only if you work at them.

For century training I recommend http://www.amazon.com/Complete-Book-.../dp/1579541992