On the Library Success Best Practices Wiki, a "Hip-Hop Resources for Librarians" wiki.
There's also a list for Public Libraries at:
http://jupiter.clarion.edu/~vmorris/UrbanFictionReadingList.htm
and a list for School Libraries at:
http://jupiter.clarion.edu/~vmorris/SchoolUrbanFictionReadingList.htm
Lastly, Wikipedia has an entry for Urban Fiction that details the history of the genre and its trends.
Source: BCALA listserv 5/05/06