Face Hugger

Simple. It attaches itself to someone's face.

Usually Nightmare Fuel from some horror film.

May be related to Face Full of Alien Wingwong.

Comics

 * The mind-control starfish of Starro the Conqueror.

Film

 * The xenomorphs from Alien. Many later examples are homages.

Toys

 * Krana and Krana-Kal of Bionicle.

Video Games

 * Gligar and Gliscor from Pokémon.
 * Metroids
 * Headcrabs from the Half Life saga.
 * Brainsuckers from X-COM Armageddon, which are used as ammunition by certain aliens in addition to appearing on their own.

Web Comics

 * In Campus Safari, Chrome's miniwhip Aurla does a good impression of one. (Played for laughs)
 * Sam Starfall pulls one of these off in an early strip of Cross Time Cafe. Hortmage finds it irritating and, maybe, disgusting.