You might know the great Phil Hartman from such voice acting work as D-list fading star Troy McClure and scumbag lawyer Lionel Hutz. Hartman appeared in 54 episodes of The Simpsons before he was tragically murdered by his wife in 1998. He also played four other characters during his time on the show, most notably Lyle Lanley from the canonical fourth-season episode "Marge vs. the Monorail." In many ways, Hartman's death signaled the end of the golden age of The Simpsons, and the show's writers wisely and tastefully retired his characters.

A six-time Emmy winner, Kelsey Grammer has lent his considerable talents to The Simpsons since the show's first season with his classic recurring character, Sideshow Bob. Many consider Bob the show's greatest peripheral character, and several of the ten episodes that have heavily featured him are among the show's best, particularly "Cape Feare" from the show's fifth season. Grammer's Frazier co-stars David Hyde Pierce and John Mahoney have also made guest appearances as Bob's brother and father, respectively.

Joe Mantegna has been voicing Springfield's most notorious mobster, Fat Tony, since the show's third season. Mantegna, who was one of only two of the show's regular guest stars (the other is next on this list) to appear in 2007's The Simpsons Movie, has had many great moments as Fat Tony, but our favorite is season six's "Homie the Clown." Here's a clip from Fat Tony's first episode, which aired shortly after Goodfellas was released and was tweaked by the writers to incorporate elements from that film.

While he does not voice any recurring side characters, Albert Brooks has been a significant contributor to the show since its first season. He is best remembered for his role as evil mastermind Hank Scorpio in the episode "You Only Move Twice," who lured the Simpson family to move from Springfield to the idyllic planned community of Cypress Creek. He also voiced bowling instructor Jacques and self-help guru Brad Goodman on the series, among others, as well as EPA Agent Russ Cargill in The Simpsons Movie.

Although he only appeared in one episode, season three premiere "Stark Raving Dad," Michael Jackson is easily the biggest of all Simpsons one-off guest stars, particularly at the time the episode aired in 1991. Cleverly, Jackson voiced Leon Kompowsy, a mental patient who believed he was the King of Pop. Jackson, who used the pseudonym John Jay Smith, wrote a song for the episode, "Happy Birthday Lisa," and also co-wrote the song "Do the Bartman" for the 1990 album The Simpsons Sing the Blues.

Danny DeVito has appeared twice on The Simpsons as Homer's long-lost, businessman half-brother Herb Powell, in season two's "Oh Brother, Where Art Thou?" and season three's "Brother, Can You Spare Two Dimes?" We prefer the first appearance, in which Homer bankrupts Herb's Detroit car company by designing a hideous and impractical vehicle. Given that the joke was that easy in 1991, it's no wonder the American car industry has fallen so hard.

Several major league baseball players made cameos in the third-season episode "Homer at the Bat," but for our money Darryl Strawberry was the best. The premise of the episode is that Mr. Burns makes a million dollar bet over a company softball game and brings in a crew of ringers, including Strawberry, Roger Clemens, Ken Griffey Jr., Jose Canseco, and Ozzie Smith. While Strawberry kisses up to Mr. Burns, each of the other ringers is kept out of the game through a series of bizarre, unfortunate, and very funny events.

Another one-off guest star, John Waters appeared as the creatively named John in the season eight episode "Homer's Phobia." John was perhaps the first openly gay character to appear on the show, and after meeting him Homer launches into a homophobic panic and becomes convinced that Bart is gay. Homer then embarks on a misguided and zany campaign to prevent Bart from being gay.

In season five's "Rosebud," which Entertainment Weekly declared the second-best episode in Simpsons history, Smithers hired the legendary Ramones to sing "Happy Birthday" to Mr. Burns. As you can see from the clip, it probably didn't go as Smithers expected. The Ramones were huge fans of the show and considered this guest appearance a career highlight.

Leonard Nimoy's two appearances on The Simpsons are wonderful because of their self-awareness of Nimoy's science fiction background as Spock on Star Trek. Nimoy first appeared in season four's "Marge vs. the Monorail," widely considered one of the best episodes ever, and then came back for season eight's "The Springfield Files." Nimoy's first appearance is the funniest, and the clip below highlights the show's madcap yet clever humor from that period.

The late, great Barry White appeared on two episodes - season four standouts "Whacking Day" and "Krusty Gets Kancelled." For those unfamiliar with "Whacking Day," the town of Springfield has a holiday celebrated by clubbing snakes. Mayor Quimby invites White to be the grand marshall for Whacking Day, but when White discovers what the holiday is about he helps Lisa drive away the snakes with a rendition of "Can't Get Enough of Your Love, Babe" recorded specially for the episode.

One of the most random guest appearances on this list, Johnny Cash lent his talents to season eight's "El Viaje Misterioso de Nuestro Jomer (The Mysterious Voyage of Homer)." Following Homer's consumption of Guatemalan insanity peppers at the Springfield annual chili cookoff, he goes on a strange trip directed only by Cash as his spiritual guide. The episode drags a bit once Homer's psychedelic journey ends, but Cash was sublime.

Tito Puente appeared in the season six finale/season seven premiere cliffhanger "Who Shot Mr. Burns." Puente's band performed a song about Mr. Burns' evil nature, which explains "Wounds won't last long, but an insulting song / Burns will always carry with him." As you can see from the clip below, hilariously introduced by Troy McClure, the animators even prepared a clip of Puente shooting Mr. Burns to help keep the real surprise under wraps.