I keep coming back to this thread without putting anything up, 'cos it's such a subjective thing. I honestly don't think there can be an 'all-time best' album, because tastes change, and it comes back to personal all-time best.
So, for whatever it may be worth, in no particular order, mine would be:
Dark Side Of The Moon
Court Of The Crimson King
Bridge Over Troubled Water
The Hissing Of Summer Lawns
Shawn Colvin Fat City
Kris Delmhorst Song ForA Hurricane
Dummy
Arcade Fire Funeral
Close To The Edge
Joshua Tree
There's something about each of these recordings that has a deep personal resonance, and that for me makes them great.