During the Credits
There are no extra scenes during the credits of Resistance: Fall of Man, but there is a little joke towards the end of the credits explaining that no mutagenic, blood thirsty, freedom-hating alien scourge were harmed in the making of the game.
After the Credits (spoilers)
There is an extra scene setting up the sequel after the credits of Resistance: Fall of Man. After the credits there is an extra scene showing Nathan Hale, who was presumed to have been killed, alive and walking through the snow with a grenade in his hand. Black-Ops are shown getting out of a helicopter and surrounding Hale as he contemplates using the grenade; however, he ends up dropping it and allowing himself to be taken by them. The scene ends with a shot of the helicopter flying off and this is where Resistance 2 picks up.