Get Black Star - "Black Star" immediately. Mos Def and Talib Kweli are some of the best underground MC's there are. Put them together and it's just pure magic.

Track suggestions - "Definition", "Respiration"

Then grab Danger Doom - "The Mouse and the Mask" to get silly with the amazing DJ Danger Mouse (of Gnarls Barkley, Gorillaz, and The Grey Album fame) and the supervillain himself MF DOOM.

Track suggestions - "Old School", "The Mask", "Sofa King"

To end it, Grab Roots Manuva - "Brand New Secondhand" for some of the smoothest raps you'll ever hear. The fact he has a slight UK/Jamaican accent gives it some extra flavor.

Track suggestions - "Clockwork", "Motion 5000"

If you could be specific about what kind of production, tempo, or style of hip-hop you want I could give tons more suggestions.