What was the last GREAT album from the 20th century?
How strictly are you defining "GREAT"
Presumably it's something from late-ish 1999, I'd vote Boredoms - Vision Creation Newsun.
There are a lot of great albums released in 1999.
Keep It Like a Secret, I See a Darkness, The Soft Bulletin, 69 Love Songs, The Fragile, Emergency & I...