Rolling Stone has a really great obituary, Muhammad Ali, Boxing Legend, Dead at 74.
In 2001 I saw the Will Smith movie Ali and liked it. More recently I liked 2013's The Trials of Muhammad Ali which focused more on his activism and legal battles than his boxing which I didn't know much about.
I had no idea he starred in his own biopic, The Greatest (1977) and will have to find it (it's not streamable on Netflix) even though the reviews aren't great. Also there's 2014's I Am Ali, a documentary based on family interviews and audio journals.
Here's another Ali tie-in to topics I typically write about, Declassified NSA files show agency spied on Muhammad Ali and MLK.