Sonic the hedgehog 3 too many times to remember and same thing for Aladdin on the Megadrive.
FF8- 3 times
Ratchet & Clank Tools of Destruction - 3 times
Uncharted Drake's Fortune - 4 times
Diablo 2 - 4 times at least
That's just a few games at the top of my head. I have completed far too many games twice as it is a common requirement for a platinum these days.