surprised so many ppl mention "London Calling"... definitely a classic album, and there are at least 12 unbeatable tracks on it, but i don't think i ever listen to all 19 tracks of it without skipping at least a couple of the "third quarter" ones...
also surprised no one's yet mentioned "Heart of the Congos"... surely the most "perfect" album (production wise) ever?
other fairly obvious ones:
Marvin Gaye - What's Going On
Curtis Mayfield - Superfly
BM&W - Survival
Israel Vibration - The Same Song
Burning Spear - Marcus Garvey/Garvey's Ghost
The Slits - Cut
Steel Pulse - Handsworth Revolution
Public Enemy - It Takes A Nation Of Millions To Hold Us Back
RATM - RATM
Roots Manuva - Brand New Second Hand
ADF - Rafi's Revenge
The Abyssinians - Satta Massa Gana (aka Forward On To Zion)
most Fela Kuti albums, given that there are usually only 2 or 3 tracks on them...