I haven't read every post so if some already already posted what I'm about to say then I second what they say.
First off, asking for the best "rap" song is where you went wrong, it all about Hip-Hop. So im going to list what is my favorite hip hop artist, songs & albums.
A Tribe Called Quest, The Roots, Pete Rock, CL Smooth, Redman/Muddy Waters, Nas/illmatic, Wu-Tang-Clan, KRS-One, Maryly Marl, Ahmad, Arrested Development, Beastie Boys, Biz Markie, Black Moon, Black Sheep- The choice is yours, Black Star, Black Violin, Blackalicious, Busta Rhymes, Brand Nubian, Camp lo- luchini & Coolie High, Common- I used to love H.E.R & The Light, Craig Mack- Get Down & Makeing Moves With Puff, Dead Prez- Hip Hop/Dave Chappelles thyme song, Digable Planets!!, Digital Underground, DJ Shadow- Swan Lake, DJ Honda, Gang Starr, Rza, Ghostface Killah, Goodie Mobb, Hi-Tek, J Dilla, Juru Tha Damaja, KEITH MURRAY!!!!!!!, Deja Vu, Lost Boys, Canibus, Lupe Fiasco, Main Source, Method Man, Missy Elliot, Mos Def, Jurassic 5, Musiq Soulchild, Nappy Roots, Naught By Nature, Timbaland, Notorious B.I.G, ODB, Onyx, Outkast, Paper Boy- The Ditty, Pharell, Pras Michel, Rah Digga-Imperial, Rappin' 4-Tay- Ill be Around, Slum Village, Smif-N-Wessun, Tag Team, N2Deep- Back to the Hotel, Wrex N Effex, Wyclef Jean, Mr.Cheeks & Im going to stop there, I hope you like it.
Word to Full Sail!