Illmatic - Nas
Any Big L, take your pick, best rapper ever.
Gangstarr - Hard to earn
Atmosphere - When life gives you lemons, paint that **** gold.
Wu-Tang - 36 Chambers.
That should give you a good variety, if your looking for some underground/more of a coastal rap.
XV - The complex (Get the mixtape, really good)
Kid CuDi - Man on the moon
Artist Spotlight - Reebok Album 1 (Alot of Lupe)
Artists to listen to. (More unknown, i can give you more)
Slug
Wale
XV
Dl Incognito
I used to have over 15k underground songs on my other laptop, but i had to wipe it and didnt get my external HDD yet so there all gone