Cannibal Corpse - Eaten Back to Life
Exodus - Bonded by Blood
Venom - In League With Satan
Bauhaus - In the Flat Field
Killswitch Engage - Alive or Just Breathing (this one should have made the list...oops :p)
Turns out, most influential albums are NOT the artist's first release - see: Slipknot, Linkin Park, AC/DC.
I'd personally argue that Piper falls more under the category of space rock than progressive rock (which I'd say applies more to the Gilmour/Waters/Wright/Mason era). Of course, it was highly influential on a lot of space rock music (as well as music that took inspiration from space rock), and even though I prefer its underrated follow-up A Saucerful of Secrets (I'm not a diehard Syd Barrett fan -- I like Piper, but I'd rate it as only like their seventh best or so), I can't deny the lasting impact Piper has had, regardless of genre classifications.
Regardless of what you think of Weezer (and I'm not really a fan outside of that album, which I think is quite good), I don't think you can deny how essential their first two albums were to the post-alternative emo bands that followed in the wake of their mid-'90s success. Whether or not that's a good thing is subjective, but influential? Certainly.
