Andrea Martin, the actress and comedienne, plays Moogie, Quark and Rom's Ferengi society defying mother, in the "Star Trek: Deep Space Nine" episode "Family Business".
Stephen Hawking plays himself in a game of poker with Sir Isaac Newton, Albert Einstein and Data in the "Star Trek: The Next Generation" Episode "All Good Things...". Hawking currently holds the position of Lucasian chair of Mathematics at Cambridge University, a position formerly held by Sir Isaac Newton and held by Data in future scenes of "All Good Things...".
Punk rocker Iggy Pop played Yelgrun, the Vorta overseer working for the Dominion, in the "Star Trek: Deep Space Nine" episode "The Magnificent Ferengi".
Kelsey Grammer of "Cheers" and "Frasier" played Captain Morgan Bateson, a captain of the Enterprise whose ship was stuck in a time loop, in the "Star Trek: The Next Generation" episode "Cause and Effect".
Kirsten Dunst, best known for playing Mary Jane Watson in the Spider-Man films, played in the "Star Trek: The Next Generation" episode "Dark Page" when she was just eleven-years-old.
Christopher Lloyd, best known for his role as "Doc" Brown in the "Back to the Future" trilogy, played Klingon Commander Kruge in the film "Star Trek III: The Search for Spock".
A young Ashley Judd played ensign Ensign Robin Lefler, a love interest and friend of Wesley Crusher, in two episodes of "Star Trek: The Next Generation" "Darmok" and "The Game."
Teri Hatcher played Lieutenant B.G. Robinson, a transporter officer who is seduced by a rogue, in the "Star Trek: The Next Generation" episode "The Outrageous Okona".
Tom Morello of Rage Against the Machine and Audioslave played uncredited officer in "Star Trek: Insurrection" and a crewman in the "Star Trek: Voyager" episode "Good Shepard"
Kurtwood Smith, best known for "That '70s Show" and "Dead Poets Society" has played several roles in "Star Trek". He played the Federation president in "Star Trek VI: The Undiscovered Country", Thrax, Odo's predecessor in the "Star Trek: Deep Space 9" episode "Things Past" and Annorax in the "Star Trek: Voyager" episode "Year of Hell" and "Year of Hell: Part 2".
James Cromwell played multiple roles in the Star Trek franchise. Most notable was his performance as Zefram Cochrane in "Star Trek: First Contact" as the first human to create a warp drive.
Nikki Cox who is best known for her role on the sitcom "Unhappily Ever After" played Sarjenka, a little girl on a doomed planet communicating with Data, in the "Star Trek: The Next Generation" episode "Pen Pals".
It is easy to forget that the Star Trek franchise has been cranking out films and shows for a LONG time. So far there have been six series, "Star Trek", "Star Trek: The Animated Series", "Star Trek: The Next Generation", "Star Trek: Deep Space Nine", "Star Trek:Voyager" and "Star Trek: Enterprise" as well as eleven feature films. Due to the large, ensemble cast and multiple plot lines per episode, this means that at one time or another an absurd number of actors have appeared in minor roles.
I'd have to say I like DS9 the most of all the Star Treks overall though.