some of the most famous rappers arent so good. jay-z has developed one of the worst vocal deliveries in all of rap even though he used to be good (vocally). nas still writes great lyrics and writes cool flows (rhythms) into his raps, but his breath control isnt nearly as sharp as it used to be.
in the 90s there were many famous rappers who were amazing. wu tang (and all their solo releases), 2pac, bone thugs (!), dmx, nas, mobb deep, the list goes on and on.
these days there is certainly an "indie rock version of rap" but lots of them arent so great. the def jux records artists are great (el-p, aesop rock, cannibal ox, rjd2), there are some great instrumental rap artists in the underground (dj shadow, blockhead, dj krush), there is some good west coast underground rap (hieroglyphics, living legends), del is good, but most of the "underground" or "alternative" artists in rap are not that great. people who listen to this kind of rap, generally, are suckers for any raps that are "scientific," any raps that complain about the mainstream, any raps with over-the-top multisyllable coordination in the rhyme scheme (people who rhyme "toasted skin monopoly" with "roasted him probably") which often forces them to make meaningless lyrics, and anyone who rhymes "lyrical" with "miracle". many of these underground rappers sound like bad spoken word poets.
many fans of underground rap have funny theories on how there is supposedly a difference between "rap" and "hip hop". sometimes its just a matter of "rap (music) is a subset of hip hop (culture)" which makes sense. but sometimes they argue that "rap is violent and dumb while hip hop is progressive and intellectual" or some other highbrow/lowbrow distinction. this is BS because most of the best rappers have been aggressive and at least somewhat "gangsta" and full of shock value: 2pac, bone thugs, wu tang, nas, dr dre and his rappers, notorious big, kurupt.
the best rapper alive right now is bizzy bone (formerly of bone thugs n harmony). he is also just about the best male vocalist alive, maybe number 2 (behind mike patton).
btw i make rap music. i make beats for this guy:
http://www.myspace.com/builtforlifesshit