Definately stay away from the poppy crap like Juvenile, Ludacris,
The only problem with getting into rap is that you may have a difficult time if you get full albums. Start with:
Anything By TC Islam
Stevie Hyper D - Try to find Kenny Ken and Stevie Hyper D at Mach 1 Jungle set
Tupac - Life Goes On
The Roots - "You Got Me" off of "Things Fall Apart"
"If I get Locked up Tonight" by Eminem (it's pretty short), it will completely change your respect for his abilities.
3-6 Mafia - Ass and Titties ------Just kidding