Underground hip hop music maintains the core compentencies that mainstream artists sometime miss. Artists such as Aesop Rock, Murs, Atmosphere and Blackalicious certainly focus more effort on creating well produced beats and thought provoking lyrics. Here's a brief list of the underground hip hop music I'm listening to right now.
Float by Aesop Rock. This classic hip hop album screams "underground." I've had this album for over seven years and still hear something new every time. The lyrics are among the deepest and most complex ever written, with each track unfolding new layers of meaning after repeated listens. This is certainly not the most easily accessible rap, and you shouldn't expect much after a single cursory listen; like all of Aesop's albums, it only gets better with time.
The Undisputed Truth by Brother Ali. Since his album Rites of Passage dropped in 2000, I've been a fan of this rapper. Underground hip hop music goes in many directions, and while rappers like Aesop Rock stretch its boundaries, Brother Ali returns to its roots, using call and response over classic breakbeats. This is one of my personal favorite rap albums, ever.
Blazing Arrow by Blackalicious. This album is one of the most broad musical landscapes ever produced. With the unbeatable team of Chief Xcel as producer and MC Gift of Gab, Blazing Arrow is at times frightening, inspiring and downright spiritual in its exploration of topics such as the role of blacks in America, presidential campaigns and that indescribable feeling of joy which can be found at the strangest of times. Certainly one of the highest expressions of hip hop music in the past decade.
Black Star by Mos Def and Talib Kweli. OK, so the commercial success of this album may hinder its inclusion with the underground, but the topics addressed by these two world class MCs is very underground in scope. Thorughout the album, you hear references to where mainstream hip hop is going wrong, and how the truly great rappers still come from the underground. Talib Kweli says so himself "Cats with the raw skills... they're in the underground."
These four albums are my current favorites as representations of underground hip hop music at its finest. For anyone looking to learn more about underground rap, these four are a great start, both for their musical and lyrical prowess. While mainstream artists may make more money, the underground artists are the ones who carry the torch.