I'm not sure how successful this will be, but what the hell. This is for jazz - modal, bebop, hard bop, avant garde, acid, whatever you like - but it's also for blues, gospel, soul, R&B if we're in a pinch. You can fuck off with your smooth muzak however.
What are you into? What are you listening to right now?
Personally I'm a bit of a newcomer, only having moved towards this area in the last two years or so. I've mainly been excavating the vast contributions of Miles Davis and have come to the standard conclusion he's the greatest artist of the 20th century (he or Bird). I'm also into the "holy trinity" of John Coltrane, Pharoah Sanders and Albert Ayler, although I find Ayler really really difficult. Cecil Taylor and Sun Ra about round it off for the weird shit, and after that I like Horace Silver, Ark Blakey, Thelonius Monk and Sonny Rollins.
On a side note (perhaps just to spark discussion) I read a contentious statement in the letters of Federico Garcia Lorca when he was staying in New York, claiming that the US has virtually no major cultural contributions besides what their black community, with whom he felt an affinity, had produced. While he overstates his case it's inarguable that there is at least a blues route for almost all 20th century rock and pop music, and it seems to me that the likes of Cream and Led Zep are actually a bit of a step down from the folk and blues they appropriated. Howlin' Wolf is the man.