On the Road vs Dharma Bums, etc.
Sorry to disagree with previous postings but I don't think reading On The Road first is necessary. Dharma Bums was the first Kerouac book I ever read and it completely pulled me into the Kerouac world. No, it isn't mad experimental prose or "spontaneous bop prosody" but that's a good thing for a Kerouac first timer. What Dharma Bums offers is a portal into Kerouacian Zen literary ramblings and wanderings, and presents the engaging character of Japhey Ryder (Gary Snyder), a sort of buddhist antithisis to the crazed, speed-talking Dean Moriarty.
Incidentally, too, the published version of On The Road does not really do justice to Kerouac's famed experimental spontaneous prose. Visions of Cody is really the Road volume that wasn't published in JK's lifetime and marks real run-on enthusiastic experimentalism. But DON'T start with Cody, whatever you do. While some of the passages are absolutely fantastic and conjure a vast and largely gone red brick neon America, it is a difficult book and will likely frustrate a first time Kerouac reader.
Caveat to that thought, though. Pick up the Visions of Cody books on tape (read by, of all people, Graham Parker, a British rocker). I was VERY skeptical of this until I listened to it. It's Cody distilled onto 2 cassette tapes, some absolutely incredible passages, and the reading by Parker totally captures the feel and rhythms of Jack's prose.
Dharma Bums first, then Road. That's my vote.