Second.

When the Levee Breaks. I heard there was a group of Led Zep fans that drove throgh New Orleans days after (and during the clean-up) of hurricane Katrina. Pretty screwed up, but appropriate.

I'm kind of surprised how many times "Achilles Last Stand" was mentioned
in this thread, especially since IIRC, "Presence" was one of Led Zeppelin's
poorest selling albums.

As others mentioned, it's impossible narrow a "greatest" list to a single pick.
Here's my favorite choices:

1) Achilles Last Stand - one of my favorite Jimmy Page solos
2) The Lemon Song - for the epic bass lines
3) The Rover - features my other favorite guitar solo
4) Dazed And Confused (live version on SRTS)
5) Song Remains The Same

since i've been loving you

No way I could pick just one song. It's a struggle just to get down to top ten...
Gallows Pole
Bron-Yr-Aur Stomp
Battle of Evermore
Four Sticks
When the Levee Breaks
Houses of the Holy
In My Time of Dying
Whole Lotta Love
Ramble On
Dazed and Confused

Man, I'm already second guessing it...tough one.

Squeeze me baby, till the juice runs down my leg.
The way you squeeze my lemon, I'm gonna fall right out of bed.

Snap.

it's ripped off from a Robert Johnson song, anyway - Travellin' Riverside Blues, I believe it was

Gonna go with Kashmir. It's the first Zeppelin song I ever heard, and I can't say I really enjoy a huge amount from them.

Oh didn't know that. Haven't heard Mr. Johnson in ages. Dirty ol' man.

All My Love