When roasting coffee beans the primary goal is to get the green coffee beans to change color to that dark rich color we all know and love, as well as start the chemical reactions that give coffee its characteristic aroma and flavor.
Contrary to initial guess (I always though darker roasts meant more caffeine and a more potent taste) lighter roasted coffee beans are more acidic and have a higher caffeine content. Dark roasts are less sharp in flavor and also contain less caffeine.
A couple common roasts are: American/Light roast- most common for the Eastern US; often used in professional coffee tasting. City/Medium roast- most common for Western US. French/Espresso- color is dark brown and have less acidity. Spanish roast- darkest roast available, with a “burned” flavor.
http://coffeetea.about.com goes into more detail about each type of roast.
+Plus: Coffee has the same amount of antioxidants as three oranges, which help prevent cancer and heart disease. So drink up!
And stay caffeinated,