It's been a few years since I heard the original version of some of
these, but it was an eye opening experience. Like I said, in many
case it wasn't so much the songs were stolen, it was more like they
were the same songs. This list looks pretty good, quoted from this
page: http://www.warr.org/zep.html
I've never thought that "Taurus" by Spirit sounds much like Stairway
to Heaven though, so I disagree with that one at least.

*****

Babe I'm Gonna Leave You" - A folk song by Anne Bredon, this was
originally credited as "traditional, arranged by Jimmy Page," then
"words and music by Jimmy Page," and then, following legal action,
"Bredon/Page/Plant."
"Black Mountain Side" - uncredited version of a traditional folk tune
previously recorded by Bert Jansch.
"Bring It On Home" - the first section is an uncredited cover of the
Willie Dixon tune (as performed by the imposter Sonny Boy
Williamson).
"Communication Breakdown" - apparently derived from Eddie Cochran's
"Nervous Breakdown."
"Custard Pie" - uncredited cover of Bukka White's "Shake 'Em On Down,"
with lyrics from Sleepy John Estes's "Drop Down Daddy."
"Dazed And Confused" - uncredited cover of the Jake Holmes song (see
The Above Ground Sound Of Jake Holmes).
"Hats Off To (Roy) Harper" - uncredited version of Bukka White's
"Shake 'Em On Down."
"How Many More Times" - Part one is an uncredited cover of the Howlin'
Wolf song (available on numerous compilations). Part two is an
uncredited cover of Albert King's "The Hunter."
"In My Time Of Dying" - uncredited cover of the traditional song (as
heard on Bob Dylan's debut).
"The Lemon Song" - uncredited cover of Howlin' Wolf's "Killing Floor"
- Wolf's publisher sued Zeppelin in the early 70s and settled out of
court.
"Moby Dick" - written and first recorded by Sleepy John Estes under
the title "The Girl I Love," and later covered by Bobby Parker.
"Nobody's Fault But Mine" - uncredited cover of the Blind Willie
Johnson blues.
"Since I've Been Lovin' You" - lyrics are the same as Moby Grape's
"Never," though the music isn't similar.
"Stairway To Heaven" - the main guitar line is apparently from
"Taurus" by Spirit.
"White Summer" - uncredited cover of Davey Graham's "She Moved Through
The Fair."
"Whole Lotta Love" - lyrics are from the Willie Dixon blues "You Need
Love."

******

Also, here's a link to an album sold on Amazon, The Blues Roots of Led
Zeppelin. Just perusing the titles should sound familiar if you're a
big fan of Led Zeppelin. As one of the reader's comment says, "along
with the roots, they may have stolen the whole tree".

Again, despite of this, I still think Zeppelin is a great band,
perhaps only second to the Beatles. The Beatles lifted a few things
themselves, like the bass line to I Saw Her Standing There, which is
from a Chuck Berry song (I think it was called "I'm Talking About
You".
http://www.amazon.com/Blues-Roots-Led-Zeppelin/dp/B00004Y333

And the track list:

1. When The Levee Breaks - Memphis Minnie
2. Sugar Mama - Sonny Boy Williamson
3. Jesus Gonna Make Up My Dying Bed - Josh White
4. Nobody's Fault But Mine - Blind Willie Johnson
5. Traveling Riverside Blues - Robert Johnson
6. The Girl I Love She Got Long Curly Hair - Sleepy John Estes
7. Shake 'Em On Down - Bukka White
8. I Want Some Of Your Pie - Blind Boy Fuller
9. Gallis Pole - Leadbelly
10. My Mama Don't Allow Me - Arthur Crudup
11. My Baby I've Been Your Slave - Sonny Boy Williamson
12. Fixin' To Die - Bukka White
13. Boogie Chillen - John Lee Hooker
14. Lone Wolf Blues - Oscar Woods
15. Got The Bottle Up And Gone - Sonny Boy Williamson
16. Truckin' Little Woman - Big Bill Broonzy
17. Going Down Slow - St. Louis Jimmy Oden