The world has been filled with music. Following the Grateful Dead and my time at MIT opened my ears to lots of music.
Some music that I think is worthwhile to check out is:
Although he was the bass player for the Grateful Dead, Phil Lesh's musical training was in 20th Century performance / electronic music composition.
Over 30 years ago a group of friends started playing music together in East LA. After scoring a major pop success in 1987 with their remake of La Bamba, Los Lobos followed up with an album of Mexican folk music, the music they grew up with.
Since then they have scored movies, experimented with production electronics, put out an album of children's music, and played live blues, rock, Mexican folk from the heart and the seat of their pants.
Be sure to check out LobosBase1983-2010 for setlists of Los Lobos' live shows.
I feel privileged to have been taught by one of the preeminent contemporary composers while at MIT. His classes on 20th Century Music and Musical Institutions were intriguing, ear opening, and provocative. The intersection of art, commerce, and personal politics in symphony halls, opera houses, ballet theaters, and chamber rooms from Boston to LA (where Harbison served as Composer in Residence for his close friend Andre Previn) is one that inexorably shapes the ears of Americans and the livelihoods of contemporary composers.
His opinions, scheduled listenings to composers including Schoenberg, Cage, Stravinsky, Varese, Carter and Maxwell-Davies, and Harbison's own off-the-beaten-path blues piano convinced me that all true art comes from the same spot in the human psyche, no matter how varied the voice that portrays it.
As the link between 19th and 20th century music, Gustav Mahler stands as an icon. Several of his symphonies can fill a complete symphonic program, yet his meticulous nature filled an hour and a half of music with intended precision. Mahler composed, conducted, and re-composed his own works until he was satisfied with them or was distracted by a new piece of music.
Because Mahler's dayjob was an operatic conductor, his works have posed a great challenge for contemporary orchestras. I feel lucky to have attended an outstanding performance of Mahler's 9th by the Boston Symphony Orchestra with Kent Nagano covering for Seiji Ozawa. As for recordings I would recommend the recordings with Claudio Abbado conducting (although the recordings with Mahler's friend Bruno Walter conducting are worth exploration).
I also suggest avoiding the Leonard Bernstein performances. Although Bernstein imparts some of the Romantic passion into the pieces, he tends to lack the subtlety that brings out the intricate voicings that truly make Mahler wonderful.
I would also suggest avoiding Mahler's 6th Symphony at holidays. I know of no other piece of music that can impart a feeling of hopelessness and utter despair as this symphony. To paraphrase almost 2 hours of music, life sucks and then you die. The struggle may be valiant, but you will be struck down by the hammer blows from on high.
After a few years of the composer's life with a terminal disease, Mahler's hero by his 9th Symphony has come to terms with this inevitable finality and the last movement is spent at peace with self and world.