Well a couple.
Cabaret, for one...my aunt played the soundtrack while driving me to Nursery School everyday, it was the first showtune-like music I was ever introduced to.
It's a pretty common answer, but Rent as well. It was the first show I really fell in love w/, first cast recording I ever bought, first show I saw more than once. I adored the music, loved the passion and feeling behind it, and the messages, and the whole idea of taking a terrible situation but making the show essentially happy and celebrating, and just really is a good example on how to live life.
Wicked inspires me. Everytime I am going through a tough time or I have a very difficult thing to do, I listen to and/or sing Defying Gravity.
West Side Story showed how touching and magical theatre could be with all of its parts working together perfectly
"If there was a Mount Rushmore for Broadway scores, "West Side Story" would be front and center. It snaps, it crackles it pops! It surges with a roar, its energy and sheer life undiminished by the years" - NYPost reviewer Elisabeth Vincentelli