You could cite any number of reasons as to how Germany became the economic powerhouse it is today, but first I'll give you a bit of information on a key figure behind the German Economic Miracle (Wirtschaftwunder), which helped get Germany back on its feet.
Ludwig Erhard served in several economic positions during the 3rd Reich, but refused to become a Nazi. In 1942, he realized that Germany was going to lose the war, and began drawing up plans for post-war reconstruction, which were based around the scenario of Germany losing the war. These plans became the blueprint in reviving the German economy. Erhard believed that cutting taxes drastically, reforming the currency (Reichsmark -> Deutschmark), and removing price controls would revitalize the economy.
Cutting taxes resulted in the German population paying less money to the government, and allowed the to retain more of the money that they earned. This left them with more money to buy what they needed, and not spend long hours foraging for the food and supplies they needed to survive. It also allowed them to buy more of what they needed.
Reforming the currency, which removed the worthless Reichsmark, and replaced it with the stronger Deutschmark, did wonders for the economy. It cut down on inflation by reducing the amount of money in circulation, and gave Germans more buying power with their stronger currency. This also helped increase production, because now that the money was worth more, it was worthwhile to go to work to earn that money. This increased the output of goods and services, which is generally good for a struggling economy.
During the war, the Nazi government placed price controls on many goods, which allowed them to purchase the things they needed to make war for very cheap. This hurt businesses, and didn't make it worthwhile to produce their goods. With the removal of these price controls, companies had more freedom to run their operations, and were able to set their goods at a price more beneficial to them, yet low enough for consumers to want to buy them. This gave them an incentive to produce more goods, and was a help in eliminating the rampant shortages that plagued Germany.
The Marshall Plan actually didn't do a whole lot to help Germany. At its peak, it only provided 5% of Germany's national income. Plus, Germany was paying billions in reparations and occupation fees in order to help keep the occupying Allies funded.
There are many other reasons to help explain why Germany was able to pull of its economic miracle and become an economic powerhouse in today's economy, and these are only a few. I did answer a question similar to this one a little while back, if you wanted to look at that too. It deals with Germany's relatively good economy after reunification, but a couple of the points can help to explain your question too.http://answers.yahoo.com/question/index;_ylt=AsWSm.UMAB.IO0jvq.lIQBPty6IX;_ylv=3?qid=20130307094540AAY49QY
Also, if you look up "German Economic Miracle", you should be able to find quite a bit of information.
Sorry if everything is a little scattered and confusing :( I hope this at least helped!