I think as long as you listen and know who Tupac, Notorius BIG, Jay Z, and Nas, are... you are well on your way.
Although now hip hop music has changed a bit so there are other new rap artist such as Drake.
Lil Wayne is not new but he has blew up in the past couple of years so you definently need to know who he is.
Also, MTV posted the top 10 rappers of 2009. That list will help.
A website called Rate Your Music will help. You can type in a decade or year and it will give you a list of artist and songs posted by people. (Such as 90's HipHop).
Good Luck... You've entered the darkside!