R.E.M.'s entire catalog -- the I.R.S. albums, the Warner Bros. albums -- has been remastered and is now available on iTunes. That's not really the news here. Artists do stuff like this all the time.

The big news is that a s--- ton of the band's stray tracks over the years -- B-sides, leftovers, etc. -- have been compiled and are now available for download too. And it's a treasure trove for fans.

Newly remastered versions of classic albums like 'Murmur,' 'Document' and 'Automatic for the People' are collected in bundles called 'Complete I.R.S. Studio Albums' (six records) and 'Complete Warner Bros. Studio Albums, Vol.1' (five records). Five other remastered albums from the band's Warner Bros. years are also available separately.

Additionally, two new rarities sets -- 'Complete Rarities - I.R.S. 1982-1987' and 'Complete Rarities - Warner Bros. 1988-2011' -- fill in all the missing pieces. The I.R.S. collection includes 50 tracks; the Warner Bros. set features a whopping 131 songs. That's a lotta R.E.M.!

The rarities collected on the two sets include everything from the original single version of the group's debut single 'Radio Free Europe' and a cover of the Velvet Underground's 'There She Goes Again' to a dance mix of 'Shiny Happy People' and 'The Great Beyond,' which they wrote and recorded for the 1999 Andy Kaufman biopic 'Man on the Moon.'

These new remasters follow the recent release of 'Unplugged: The Complete 1991 and 2001 Sessions,' which includes the songs R.E.M. recorded for the MTV show.

Speaking of R.E.M. rarities, here's one of our favorites: an alternate mix of 'Sitting Still' recorded during the 'Murmur' sessions: