Top selling albums of all time
Keeping track of worldwide sales of albums (technically 'titles,' which would primarily include albums, cassettes, and cd's) has always been a haphazard task. You're likely to see phrases such as 'is believed to have sold' or 'has likely reached' to describe worldwide sales. I found a few different examples in a Wikipedia entry, a short list from Retrodawg, and an highly ambitious and detailed posting from UKMIX forum member Edu.
For a more precise reading (and more relevant to North Americans), the Recording Industry Association of America (RIAA) keeps a fairly up to date list of U.S. sales. This is a reliable list for people to refer to if ever in a bet:
(million units sold)
(29) Eagles - Greatest Hits, 1971–1975
(27) Michael Jackson - Thriller
(23) Led Zeppelin - Led Zeppelin (IV)
(23) Pink Floyd - The Wall
(21) Billy Joel - Greatest Hits volumes I & II
(21) AC/DC - Back in Black
(20) Garth Brooks - Double Live
(20) Shania Twain - Come On Over
(19) The Beatles - The Beatles
(19) Fleetwood Mac - Rumours
Here's the top 100.
In the new age of music proliferation, it's becoming harder to track, and sell, what is soon to be the anachronistic concept of 'albums.' Aside from a little place hopping, I don't see this list changing much. Double Live and Come on Over are both about ten years old, and everything else on the list is at least twenty. Based on the drastic changes in technology and the producer-consumer relationship of the past ten years, the concept of albums (or cd's) will soon fade from the common public, rendering best seller lists like these the equivalent of statistics from a nearly defunct sport.