There are quite a few historical events whose date I always remember by reciting a classic rap lyric:
The L.A. Riots: "April 29th was power to the people, and there might just be a sequel.." - Ice Cube (Wicked)
The Death of Biggie Smalls: "That s*** was the worst rhyme I ever heard in my life, cuz the greatest rapper of all time died on March 9th" - Canibus (2nd Round Knockout)
The Million Man March: "Slangin bean pies and St Ides in the same sentence, shoulda repented on the 16th of October.." - Common (The Bitch in Yoo)