I'd also suggest Guru's Jazzmataz series of albums, and his Streetsoul album. Great hip-hop played by some jazz legends. Really smooth, mellow stuff. Might also be worth checking out some of the music behind hip-hop. I'd recommend The Chi-Lites (you'll be amazed how many of their songs you'll recognize), Gil Scott Heron, Curtis Mayfield and Marvin Gaye. There's also The Pimpz of Change who are worth listening to, despite not ever having any material written or recorded.