These three greats are from the birth of R n R: It is hard to pick one, but First, Second, and Third are :

1)   Johnnie Johnson, RIP ( Chuck Berry's original influential piano man " Johnny B. Goode " ).

2)   Little Richard 

3)   The Killer - Jerry Lee Lewis. 

Any latter day nominees?

From the past I'd add Ray Manzarek of The Doors to that list

Geddy Lee

Not known for keyboards but!!!!!

Jackson Browne, Carole King, Elton John, Billy Joel, Christine McVie.

great choice on carole king! how about billy joel? elton john?

Warren Zevon, now and forever. Writer and performer of one of the most recognizable piano riffs in rock. Ahooo...

I think Elton, Billy, and Carole are really stretching the rock n' roll definition. Not that I don't like some of their songs.

Ah, that was "Werewolves of London" ! 

Okay,  Fats Domino, Professor Longhair, Dr. John, Huey Smith (let's hear it for New Orleans!!!), Nicky Hopkins, Ian MacLagan, Bill Payne, Bob Andrews, Steve Nieve, and Terry Adams!!!  (Manzarek is a fine organist, not that well known for his pianny pumpin') Oh, & Leon Russell!

Greg Allman

Greg Allman

 Wellll, as with Manzarek, Gregg is known as an organist. Allman Brothers pianist Chuck Leavell (most prominent on the post-Duane Bothers & Sisters) has been playing with the Stones for about 15 years.

Huey Smith eh Suave- " Don't you just know it ". Dude, you must have been like 2 years old then !!

Rick Wright - Pink Floyd

Keith Emerson - Emerson, Lake and Palmer

Thank You. Hands down. Keith Emerson is the greatest keyboardist rock and roll has ever known.