There weren't that many double LPs made in the studio. Not all the greatest bands/artists made theirs - The Who didn't, Creedence didn't, ZZ Top didn't, and so on.
I surely forgot a few gems here, but you can always click on the "Other" option and explain your choice.
To me, Electric Ladyland is the most awesome, it's bigger than Physical Graffiti; but my vote goes to Exile on Main Street, a diamond IMO.