I also highly recommend the BMW box set "Songs of Freedom".
Another great set to check out is "The History of Jamaican Music, "Tougher Than Tough" It follows the progression of Jamaican music from rock steady, ska and into the various permutations of reggae music (dancehall, dub, etc.)
The below listed are, imo crucial for the serious reggae fan:
Burning Spear "Man In The Hills/Dry and Heavy" (finally remastered and offered as a twofer)
Burning Spear "Marcus Garvey/Old Marcus Garvey"
Burning Spear "Living Dub Vol. 3" The roots consious Spear never disappoints. These are works from his early period and are quite essential.
Augustus Pablo "East of The River Nile" and the previously mentioned "King Tubby Meets The Rockers Uptown" (both remastered) Haunting, far east sounds by the late Mr. Horace Swaby. A melodica magician.
Israel Vibration "Strength Of My Life" Vibes rule!
Mighty Diamonds "Right Time" great harmonies
Gregory Isaacs "Night Nurse" The Cool Ruler is Jamaica's Marvin Gaye
Steel Pulse "True Democracy" British reggae
U-Roy "Dread Ina Babylon" The original toaster
Aswad "A New Chapter In Dub" Hard to find, but well worth seeking out.
Bunny Wailer "Sings The Wailers" The original Wailer, Bunny does the early Wailer songs proud.
Yabby U- "King Tubby's Prophesy In Dub" Mystical, mind and body music.
Warning, make sure when listening to any of the above that you have cans that can handle significant bottom end as well as a long extention cord, as you will not be able to sit in you chair once the riddims start.
Go dere.