Even cheap mp3s on iTunes cost money, and it can be daunting to a financially challenged music fan to build a library of music that they’re really only curious about and not sure about just yet. In the Essential Download Series, we’ll take a look at groundbreaking and influential artists from each of music’s three classical ages and give you a place to start your own exploration of their music. In the second installment, we’re going to stick with classic British rock and give you the 411 on Essential Downloads for The Who.