King Triton of Disney's The Little Mermaid has an awful lot of similarities to Poseidon's son, Triton, the merman. Also, King Triton has a magic trident like the god of the sea, Poseidon.

The planet Neptune is named after Poseidon's Roman counterpart.

NEPTUNE is the name of project in Canada that is creating an underwater research network, which is connected directly to the Internet (source).