Great Organists in Rock

Tom Coster, of Santana fame, has to be on this list.

Bill Payne - Little Feat
Reese Wynans - SRV
Jimmy Greenspoon - Three Dog Night

Hammond B3 is THE organ of merit.
No EJ jokes! Not mouth organ nor even skin flute.
Grow up, people!

chuck leavell he's got to be on the list. He's played with everybody.

All Hammond players - but then I am biased

Jean-Jacques Kravetz (Frumpy / solo)
Jeff Beer (Odin)
John Tout (Renaissance)
Vincent Crane (Atomic Rooster / Crazy World of Arthur Brown)
Paolo "Apollo" Negri (Wicked Minds / Link Quartet / solo)
Par Lindh
Pete Robinson (Quatermass)
Thomas Bodin (Flower Kings)
Mike Mangan (Big Organ Trio)
John Freund (Bigger Than a Breadbox)
John Novello (Niacin)
Graham Field (Fields / Rare Bird)
Julian Jay Savarin (Solo / Julian's Treatment)
Fred Hellman (Kvartetten Som Sprängde)
Gianluca Gerlini (London Underground)
Eric Malmberg (solo)
Gerald Dellmann (Satin Whale)
Oskar Lundström (Siena Root)
Tillbjörn Persson (Sound Express)
Terry Howells (Still Life)
Rick van der Linden (Trace / Ekseption)
Fred Van Zegveld (solo)

These all have shown to have superb skill either over the course of a career of perhaps on a single album.

Also see my list on RYM (if anyone's remotely interested)
http://rateyourmusic.com/list/Crazyworldof/hammond_fest