Common's album BE is really easy to get into so I'd reccommend that as one of first albums for you to check out, along with The Roots - How I Got Over and Game Theory
then move onto whatever has been mentioned here, and also:
Outkast - Southernplayalistic, ATLiens, Aquemini and Stankonia
Wu Tang Clan - 36 Chambers
GZA - Liquid Swords
Raekwon - Only Built 4 Cuban Linx...
Ghostface Killah - Ironman and Supreme Clientelle
then if you feel like moving to more experimental, or a less "mainstream" style, check out artists associated with Rhymesayers and Rawkus Records, and maybe a couple of albums released on the Def Jux label too, though I wouldn't dive into any of them without accustuming yourself to the majority of stuff already listed here




