Note: These are the numbers from the RIAA for the U.S.
I found the following for worldwide numbers but I don't know how old this data is (I found it here
http://www.everyhit.com/recordalb.html):
"Thriller" - Michael Jackson (54 million)
"Black In Black" - AC/DC (42m)
"Their Greatest Hits 1971-1975" - The Eagles (41m)
"Saturday Night Fever" - (Soundtrack) (40m)
"The Bodyguard" - (Soundtrack) (37m)
"Bat Out Of Hell" - Meat Loaf (37m)
"Dark Side Of The Moon" - Pink Floyd (35m)
"Come On Over" - Shania Twain (35m)
"Sgt. Pepper's Lonely Hearts Club Band" - The Beatles (32m)
"Dirty Dancing" - (Soundtrack) (32m)
This list is scary.