Along with the well known D's
Edwar D. Teach
Gol D. Roger
D Ragon
Portugas D Ace
Jaguar D Saul
I found these other D's
Dracule Mihawk -> D. Racule Mihawk
Fullbody -> FullBo D.
Alvida -> Alvi D. A
Dalton -> D. Alton
Dory -> D. Ory
Sodom -> So D. Om
Spandine -> Span D. Ine
Spandam -> Span D. Am
Doc Q -> D. Oc Q
Doctor Kureha -> D Octor Kureha
Don Krieg -> D. On Krieg
Donquixote Doflamingo -> Donquixote D. Oflamingo
Crocodile -> Croco D. Ile
Axe-Hand Morgan -> Axehan D. Morgan
Miss Goldenweek -> Miss Gol D. Enweek
Miss DoubleFinger -> Miss D. OubleFinger
Gedatsu -> Ge D. Atsu
Kumadori -> Kuma D. Ori
Looks like there are a lot more D's than we once thought. Luffy's family is pretty huge.