What are some good resources about theoretical strategic planning?

I suggest Michel Porter's books "Competitive strategies", "Competitive advanateg", & "Competitive advantage of nations". There is also a lot of very useful material on the Internet. You just search for "strategy".

Six sigma (green, black belts & master) certification is well known as the best practical guide to the strategic planning which gives its user the both advantages, certification & knowledge.
Otherwise, there are so many resources you can read like porter's, game theory & model thinking.
But, I need to mention an important point which you need to have a full practical vision about the operations of the business you will plan for it strategically to make your plan doable & your targets really achieved at the end not like those liars who write great literary plans full of dreams & illusions but with no results at the end.

I like "Successful Strategy Execution' by The Economist and Michel Syrett.
It clearly shows how to keep your business goals on target.
You also need "Leading Change" by Kotter.

by definition planning is one of the fundamentals of modern life .
strategic planning helps determine the direction and scope of an organizations over the long term its also a systematic process of envisioning a desired future , and translating this vision definig the goals or objectives