Rubber Soul by Beatles

This was the album that saw the Beatles transition from a jangly Merseybeat band into something much more ambitious. With the help of George Martin, they started playing with different instruments (sitars and fuzzed out bass), genres (country!) and studio effects. Lyrically they were a long way from hand holding romance with songs about dysfunctional relationships and existential angst, and the still shocking Run For Your Life as an album closer.