I would say mine is (not in order):
Kiss-Alive I - Really launched the career of one of the biggest bands in the world
Peter Frampton-Comes Alive - Changes how the music business worked due to its sheer volume sold
Johnny Cash-Live at Folsom Prison - First; don't was all wish we were a cool as him? Also, it was a seminal show and remade his career.
Led Zeppelin-Song Remains the Same - Not sure I need to explain this one....
Lynyrd Skynyrd-One More from the Road-A great rock-n-roll record and gave us the long(er) form version of Freebird.