Before I start I just want to say I really like Eminem good albums.. his last 3 not so much.. kind of sold out imo. He's still a top tier mainstream rapper and I learned about a lot of who he mentions in his songs but his just not too good anymore.
With that said I'll put up my list and I'd also like to get some other opinion/lists or some white rappers I may not of heard of.
One of the best imo, his lyrics may be confusing so you have to interpret what he means.
Albums to check out
not my favorite but really good
Some people say "The Ugly Truth" is one of the best underground rap albums of all time
Pretty good, I don't see how someone couldn't like the song "yesterday".
R.A. The Rugged Man and Vinnie Paz
Other honorable mentions, havent really heard a lot from these guys so throw some songs at me.
EI-P and Necro (Heard a lot of their producing)