Pat Matheny is a modern jazz player at the current end of the spectrum. I don't like him all that much myself. I think he's kind of boring. I wouldn't start with him in exploring modern jazz, which I consider as really starting with bebop in the late 1940s, early '50s. (Others would probably disagree.)
Here are 10 CDs you might try:
Dizzy Gillespie, 'Shaw Nuff, Collectables. Gets you a taste of bop.
Thelonious Monk, Genius of Modern Music, Vol. 1, Blue Note. In a sense he his the father of modern jazz.
Miles Davis, Kind of Blue, Columbia. Essential modern jazz from its blossoming.
Sonny Rollins, Saxophone Colossus, Prestige. After-bop classic.
John Coltrane, Crescent, Impulse. A seminal work from a seminal modern jazz artist and his greatest group.
Charles Mingus, Black Saint and the Sinner Lady. Mingus more than anyone employs the big band-era tools of Duke Ellington and his partners in a smaller group modern jazz setting.
Miles Davis, In a Silent Way, Columbia. The start of his experiment in "fusing" rock-like electrical instrumentation with jazz.
Steven Bernstein, Millenial Territory Orchestra Vol. 1, Sunnyside. Fun music and interesting because he turns forms used by '20s and '30s, "old" jazz territory bands to decidedly modern purposes.
Branford Marsalis, Braggtown, Marsalis Music. I think this artist and this group are the tightest on the landscape right now.
Ornette Coleman, Sound Grammar, on his label of the same name. It won the Pulitzer Prize yesterday.