Oprah Winfrey, "Believe in the Stars," Season 3, Ep. 2

With the help of a sedative provided by Jack to make her flight easier, Liz becomes convinced that she's seated next to her beloved Oprah Winfrey on the plane, leading to a burst of insane oversharing and pleas for help in dealing with her latest Tracy and Jenna problem. After surreptitiously smelling Oprah's hair, Liz proceeds to confess to her bemused seatmate that, among other things, "I eat emotionally and one time at summer camp I kissed a girl on a dare but then she drowned." When our heroine goes back to the office conveying Oprah's messages about the greatness of calypso, paisley and sweater capes, she realizes post-pill haze that she hadn't actually been sitting next to the media empress after all but rather a 12-year-old girl named Pam (Raven Goodwin). Pam nevertheless ends up solving Liz's problems while providing another skewering of Liz's well-meaning but often awkward relationship to race in an episode that showcased Oprah's fine comic timing when muttering to the alarmed air hostess to "please stay close."

James Franco, “Klaus and Greta,” Season 4, Ep. 9

Sometimes James Franco’s ego can be too much to bear, but when he plays a deranged version of himself in love with a Japanese body pillow he’s one of the greatest things “30 Rock” has ever seen. In order to debunk the rumors of his romantic fetishization of his stuffed darling "Kimiko," Franco engages in a fake relationship with Jenna. She’s ecstatic, of course, swooning over staged kisses and the idea of wearing Franco's t-shirt in public, but he really just wants to go home to his man-made object, which "we never love," right? From the TGS office to a nightclub dancefloor to a sort of threeway in Liz’s bed, Kimiko goes wherever Franco does and Franco is so serious about it all it’s impossible not to love him in the role.

Will Ferrell, "Lee Marvin vs. Derek Jeter," Season 4, Ep. 17

Liz's high-minded feminism was always getting tweaked by "30 Rock," including in this episode in which she learned from Pete that the only reason what was formerly known as "The Girlie Show" got greenlit by NBC in the first place was due to complaints the network received after airing something called "Bitch Hunter." Fey's former "Saturday Night Live" cohort Ferrell stars in the uproarious cut-away clip of the show, which sees him kicking down the door to a women's restroom, brandishing a gun and yelling "Happy birthday, bitches!" The gag was good enough to be used as a callback in the season four episode "The Moms," and later in season seven in a joke about pop-up ads.

Margaret Cho, "Everything Sunny All the Time Always," Season 5, Ep. 22

As both the now-deceased North Korean dictator Kim Jong Il and his son Kim Jong Un, Margaret Cho -- of North Korean descent herself -- made a series of cameos that offered impersonations nearly identical to the infamous ones she does of her mother in her standup. In the world of "30 Rock," they involved a ridiculous (mostly in a good way) plot line that saw Jack Donaghy's then wife Avery (Elizabeth Banks) being kidnapped by Cho's Kim Jong Il and held in Korea for months before being forced into a sham marriage with Kim Jon Un that played out in season six's "The Return of Avery Jessup" and "What Will Happen to the Gang Next Year?" The best line from the Emmy-nominated appearances? “People of North Korea, it is your dear leader Kim Jong Il, world’s greatest golfer and movie director and best man at Tom Brady’s wedding!"

Jim Carrey, "Leap Day," Season 6, Ep. 9

Jim Carrey appeared in the faux movie portrayed in one of the daffiest episodes of "30 Rock," which involved an invented holiday tradition centered around the mythological figure of "Leap Day Williams" -- or "Leap David Williams," in the case of the Carrey character. Baffling both himself and his wife (Andie McDowell) as he grows a grey mustache and bubbles with (fake) holiday cheer, Carrey mocks his affinity for high concept studio comedies using a satiric edge on par with Jack Black's made-up "The Fatties" franchise from "Tropic Thunder." To be fair, even in his duds, Carrey tries a little harder than "Leap Dave Williams," but there's no doubt he's been offered real-life projects along these lines.

Octavia Spencer, "Game Over," Season 7, Ep. 9

Octavia Spencer made a late, great contribution to the legacy of "30 Rock" guest appearances in an episode that aired just a few weeks ago. "I'm about to start shooting my new Harriet Tubman movie and I got Octavia Spencer to play the lead, Harriet Something" is Tracy Jordan's on-screen introduction.  Playing a gloriously crazy version of herself, Spencer aims to one-up even the insanity that is Jordan, demanding rewrites to allow her character to "walk through walls" and insisting she will wear a t-shirt promoting her online poker website while shooting. It leads to both Jordan channelling Liz Lemon to get Spencer under control, and to some serious hilarity all around.