there's always one person who says '..it depends who's asking, its subjective blah blah blah'. The whole point beale probably asked the question is because (s)he'd like an idea of what other people thought. It true that you can never say which album is best, but at least give an answer rather than the usual 'subjectivity' argument.
Anyway some of my favourites, of which I personally think are 'best' albums from my lifetime are Massive Attack-Blue Lines, Prodigy- The Experience or Music for Gilted Generation (can't decide between the two), Radiohead- The Bends, Roni Size- New Forms, Rage Against the Machine- RATM, Daft Punk- Daft Punk, DJ Shadow- Endtroducing. Could go on. (its quite sad if you have one album you think is the best, means you don't listen to enough music.)