Conan O'Brien, "Tracy Does Conan," Season 1, Ep. 7
Despite not losing her virginity until her mid-20s, Liz has racked up a pretty storied romantic life, one that includes, it's heavily suggested, the former "Late Night" host. O'Brien threaded into the overall "30 Rock" mythology, from Liz's mention of having dated a "tall, gangly red-haired guy who played guitar all the time" to when she appears in a later season to have a sex nightmare about him while under the influence of sedatives. But the only face to face encounter between the two of them is in a season one episode in which they display some pretty convincing tension as exes before O'Brien has a funnier bit with Morgan in a flashback to Tracy's first guest appearance on his show, in which he chases the host around his desk attempting to stab him.
Paul Reubens, “Black Tie,” Season 1, Ep. 12
Who knew Paul Reubens could be even stranger, creepier and funnier than Pee-wee Herman? Reubens' Prince Gerhardt Habsburg, or Gerhard Messerschmit Rammstein Von Hab as Will Forte introduces him in a ridiculous accent, is a foreign dignitary bound to a wheelchair and possessed of one foot, a tiny gloved hand and a Hitleresque haircut. When Jenna, Jack and Liz attend his birthday party, he spies Jenna and immediately falls in love with her. The excitement is so much that the prince proceeds to lose an eyebrow then gulp down a glass of champagne and instantly die -- apparently from his inability to “metabolize the grapes.” One of the funniest “30 Rock” episodes ever, "Black Tie" proves that tReubens is truly a master of utter weirdness.
Nathan Lane, “The Fighting Irish”, Season 1, Ep. 17
It’s difficult to imagine the right actor to play Jack’s brother Eddie Donaghy, but Nathan Lane turns out to be the perfect fit, complementing Jack’s haughty charm with his own brand of goofy schmoozing. The siblings are similar yet entirely opposite -- Eddie lives in a homeless shelter while Jack, well, definitely doesn’t. The pair knock heads upon Eddie’s arrival, but warm up to one another as the episode goes on, bonding by reminiscing about their childhood and nonchalantly admitting to their cruel attacks on each other in the past. Jack calmly admits “I had sex with your prom date” and Eddie declares “I stole your identity,” to which Jack retorts “I microwaved your parakeet!" The usual comedic Nathan Lane plays big and melodramatic as Eddie, but it works so well with Baldwin's restraint that you wonder why the two haven’t done more work together.
Carrie Fisher, "Rosemary's Baby," Season 2, Ep. 4
What may be the greatest episode "30 Rock" ever produced -- and that's saying something -- was "Rosemary's Baby." It also produced its best line ever. in which Jack says to Liz: "Never go with a hippie to a second location." While guest star Carrie Fisher didn't deliver that phrase, she was the subject of it. Portraying Liz's childhood idol, comedy writer Rosemary Howard, Fisher is looniness perfected as she convinces Liz to quit TGS and come with her to her apartment to write a great feminist screenplay together. Which is where it all goes wonderfully wrong. “You’re just like me," Rosemary tells Liz. "You get up in the morning and smoke weed. You obsess about the Jamaican man across the hall... Help me, Liz Lemon, you’re my only hope!” Liz thankfully comes to her senses and gets her job back, promising to send Rosemary $400 a month for the rest of her life.
Al Gore, "Greenzo," Season 2, Ep. 5
The former vice president made two trips to "30 Rock," first in 2007 for "Greenzo" and then again for Earth Day in season four's "Sun Tea." In both cases, his segment ended by hilariously transforming into the environmental movement's equivalent to Batman ("Quiet! A whale is in trouble!" should be adorned on activist t-shirts across the nation). The second appearance is unquestionably the stronger one, as Gore's magical abilities to make plants materialize out of thin air don't solve the problem of his poor janitorial skills. But the best part of this running gag is that when it comes to Gore, whose crazy-sounding save-the-earth tome "The Future" recently hit stands, the parody isn't too far from the real thing.
Michael Bloomberg, "Subway Hero," Season 2, Ep. 12
In "Subway Hero," former Liz flame Dennis Duffy (Dean Winters) saves someone from certain death (much to Liz's consternation), an act that leads Mayor Bloomberg to celebrate Dennis on national television. Less an example of the mayor's acting chops than an appropriation of his celebrity, Bloomberg's cameo is nonetheless one of the better examples of the way "30 Rock" implicates the reality of New York into its universe of rampant silliness. By playing it straight, Bloomberg is hilarious. "When I say subway, you say 'Hero!'" Dennis shouts, shortly after thanking "Mayor Bloomburger." Bloomberg's look of shock as he complies isn't just a performance. Watch the clip here.