As far as concept albums go, it is tough to top 'Blood on the Tracks' by Bob Dylan.
From the opener, Tangled Up in Blue
to the finale, Buckets of Rain
, this is the ultimate break-up album. This should be required listening for anyone that has ever had relationship problems.
Radiohead certainly has put out some great concept albums, too. 'Kid A' is the pinnacle of Radiohead's conceptual success, imo.
As far as Pink Floyd goes, people will immediately point to 'The Wall' and 'Dark Side of the Moon,' as those were great concept albums, but the best, imo, is 'Animals.'
Dogs Part 1
Dogs Part 2
...just a masterpiece. Floyd's best album, imho (and that is saying a lot, being that I am a huge fan).