During the Credits
Throughout the credits features concept art and various drawings of Middle-earth including sketches of all the cast members when their names are shown individually. That was made as a suggestion by Ian McKellan when Alan Lee took a production still of each actor and presented them in their sketch form.
After the Credits
Besides the sketch of the Ring, there is no stinger after the credits of The Lord of the Rings: The Return of the King.
In the Extended Edition, the credits are longer because they include additional credits, the official LotR fan club credits and actors who appear in this version of the film in addition to the freezing shot of the Ring as soon as the fan club credits start. The fan club credits in TROTK covers three-year charter members and several cast members.