I believe Diana Ross playing Billie Holiday should have won an Oscar. Her performance was outstanding in each role as a i.e. young girl, singer, heroin addict, woman in love etc. The movie displayed i.e. black discrimination in the entertainment industry, her moms struggle as a maid not having the luxury of raising her daughter, the introduction of drugs to entertainers to maintain the rigid schedule of a performaner, the unforgiving attitude of the industry at that time if you were convicted of a felony as a entertainer, the love and support by her lover etc.   

Whoopi Goldberg without a doubt this was her
debut and she nailed the part. Whoopi deserved to have won an Oscar.
Twenty-seven years later The Color Purple is still as powerful as it was when it
first hit the big screen.

When The Color Purple was passed over for the English Patient I was undone.  The English Patient was a good movie but didn’t hold a candle to the performances of Whoppie, Oprah, Danny and the rest of the cast of The Color Purple.  

I’m gonna go a little old school with some of these:
Louise Beavers in “Imitation of Life”
Cicely Tyson in “Sounder”
Dorothy Dandridge in “Carmen Jones”
Angela Bassett in “Waiting to Exhale” & “Malcolm X”
Jada Pinkett in “Bamboozled”
Viola Davis in “Doubt”
Alfre Woodard in “Holiday Heart”
Diahann Carroll in “Claudine”
Ruby Dee in “A Raisin In The Sun”
Sanaa Lathan in “Love & Basketball”
and Anika Noni Rose should have gotten something for “The Princess and The Frog”
    I agree with most of the people here, with the exception of Thandie Newton.  I’ve never been all that crazy about her acting skills.  She’s either too intense or too mellow.