I'm by no means an expert, but as someone who doesn't listen to too much hip-hop I can tell you what I like.
2pac is 90s gangster rap. It seems like Wu Tang, BIG, Ice Cube are good recommendations for that.
If you're interested in listening to pop rap I'd recommend:
Outkast - Aquemini
Kanye West - Graduation
Kid Cudi - Man on the Moon
A little harder to get into but I'd also recommend:
Das Racist - Sit Down, Shut Up