Oswin Oswald in "Asylum of the Daleks" was a good Dalek, having tried to retain her humanity after being converted into a Dalek and thus reject the Dalek's nature.
"Rusty" in "Into the Dalek" was also thought by the Doctor to be good, having turned against its own race after having seen a star being born. However, it was soon reverted to its natural state after looking into the Doctor's mind.
Similarly, "Lumpy" was a Dalek who the Doctor thought had "seen the light", but in actual fact his circuits had intentionally been corrupted to lull the Doctor into an alliance which allowed Lumpy to collect all pieces of the Orb of Fates before returning to the Dalek-occupied Starbane and being remotely reverted to his natural Dalek state. ("The Doctor and the Dalek" (game))