One of the greatest albums ever written, and probably the Beatles greatest.
Released June 1, 1967, Sgt Pepper was one of the first albums you could consider "progressive rock", and one of the earliest examples of psychedelic rock. From top to bottom, it's superb, even Ringo's track is amazing! The highlight for me is Harrison's "Within You, Without You", which must have just blown the minds of an unsuspecting pop public back in 1967, hearing a sitar blaring through their speakers.
I could keep talking about each track, but I'd be saying the same thing about all of them. If you've never heard it before, the whole album is in the video above. If you have heard it, listen to it again!