slutfest - may 1st and 2nd with he who corrupts, tora tora torrence, pheonix bodies, swing by seven, the one am radio, textbook traitors, rats into robots, and many more http://www.poravion.com/slutfest
and, on april 16-18, this isn't exactly "hardcore" but i still think it is an important event....
hiphop generation is putting on the 5th (i believe?) annual hiphop conference in madison, wisconsin april 16-18th--it's basically all independent/underground hiphop and they always have amazing panels and speakers--chuck d came a couple years ago
check it out: http://www.hiphopgeneration.org/