While I don't consider him an authoritative source...
...David Brin has done some background on presentient beings in preperation for his "Uplift" series of books. IIRC, the following animals were listed as potential uplift candidates:
Whales (both toothed and nontoothed)
Apes (all)
Dogs
Cats
Raccoons
Elephants
and, of course, Octopuses.
In that final hour, when each breath is a struggle to take, and you are looking back over your life's accomplishments, which memories would you treasure? The empires you built, or the joy you spread to others?
Therin lies the true measure of a man.