Some of Led Zeppelin's hits were ripped off from other people, and they failed to credit them. I still like Zeppelin though.
"Dazed and Confused", music originally done by Jake Holmes in 1967. Jimmy Page stole all the music.
versus
There are others, like the intro to "Stairway to Heaven" was ripped from "Taurus" by Spirit:
versus
I know that Zeppelin also stole "Babe I'm Gonna Leave You" and only credited the original writer many, many years later after they were sued.
Another rip off I found was "Some Nights" by fun. Sounds exactly the same as Simon & Garfunkel's "Cecilia"
versus
You guys might be interested in this website:
http://soundsjustlike.com/