I'd add Madvillian, the Dead Prez albums/mixtapes, the Clipse albums/mixtapes, Killer Mike,
I'd also mention that the album format has never been the best fit for hiphop. Its, for the most part, been a single-based medium where albums are made only because that has been the economic reality of the music business. There are tons of amazing artists (even pre-'98) who never recorded a classic or an even album.