Well, Dead Man was undoubtedly his best film, but definately see:
Down By Law
Mystery Train
Night On Earth

Also Stranger than Paradise is good but isn't nearly as epic as Dead Man.

Finnish director Aki Kaurismaki is a friend and contemporary of Jarmusch, but unfortunately the only movie of his you can usually find is "Leningrad Cowboys Go America" (in which Jim Jarmusch himself has a cameo role) which is silly but good. Kaurismaki makes very good art films like:
Ariel (a jailbreak film, like Down by Law)
The Match Factory Girl
I Hired a Contract Killer
The man Without a Past

Also he must've had a hand in the final vignette of "Night on Earth" because it was set in Helsinki and all the actors (Matti Pellonpaa, Kari Vaananen, etc) are people he uses in his films.

As for Dead Man, it's a film which portrays the dark side of American history and the strivings of the American soul in a way that no other filmmaker can do, I think.

Blake was all over this theme, even without being the name of Johnny Depp's character, and the subject of Nobody's frequent utterances, I think.
It's still my favorite film.