1. Amy Poehler (SpongeBob SquarePants) United Plankton Pictures, Rachel Luna / Getty Images Amy Poehler voiced the sweet and terrifying Granny in the "Have You Seen This Snail?" episode of SpongeBob SquarePants. Gary ran away from home, only to be found by Granny, who had a history of overfeeding and killing snails. 2. Jordan Fisher (iCarly) Nickelodeon Productions, Frazer Harrison / Getty Images Jordan Fisher guest starred as Clark on the "iSpeed Date" episode of iCarly, where he participated in the speed-dating contest to take Carly to the school dance. 3. Ashley Benson (Zoey 101) Schneider's Bakery, Jemal Countess / Getty Images The Pretty Little Liars star appeared in the "Quinn's Date" episode of Zoey 101 as Candice, who Quinn tried to study for relationship advice. 4. Janel Parrish (Zoey 101) Schneider's Bakery, Emma Mcintyre / Getty Images You might recognize Janel Parrish from Pretty Little Liars or To All The Boys I've Loved Before, but before all that she guest starred as Sara in the "The Silver Hammer Society" episode of Zoey 101. 5. Lucy Hale (Drake & Josh, Ned's Declassified School Survival Guide) Nickelodeon Productions, Bryan Steffy / Getty Images Also known for her role in Pretty Little Liars, Lucy Hale went on a date with Drake as Hazel in the "Theater Thug" episode of Drake & Josh. She also appeared in the "Upperclassmen & Gross Biology Dissection" episode of Ned's Declassified School Survival Guide as Amy (pictured above), the girl Moze's crush was trying to make jealous by asking Moze to be his date. 6. Emily Ratajkowski (iCarly) Nickelodeon Productions, Dominik Bindl / Getty Images Supermodel Emily Ratajkowski guest starred as Gibby's girlfriend Tasha in the "iSpeed Date" and "iEnrage Gibby" episodes of iCarly. 7. Vanessa Hudgens (Drake & Josh) Nickelodeon Productions, Tibrina Hobson / Getty Images High School Musical star and queen of Netflix Christmas movies Vanessa Hudgens guest starred as Rebecca — a girl who was kissed by Drake when she covered for his tardiness — in the "Little Sibling" episode of Drake & Josh. 8. Austin Butler (iCarly) Nickelodeon Productions, Kevin Winter / Getty Images Austin Butler guest starred in the "iLike Jake" episode of iCarly as Jake, who offered to perform on Carly's show but ended up being an awful singer. 9. Dylan Minnette (Drake & Josh) Nickelodeon Productions, Alberto E. Rodriguez / Getty Images The 13 Reasons Why star made a brief cameo in "The Demonator" episode of Drake & Josh, where he was dressed as a pirate. 10. Dianna Agron (Drake & Josh) Nickelodeon Productions, Alberto E. Rodriguez / Getty Images Glee's Dianna Agron made an appearance in the "The Great Doheny" episode of Drake & Josh as Lexi, who went on a date with Drake. 11. Harry Shum, Jr (iCarly, Zoey 101) Nickelodeon Productions, Randy Shropshire / Getty Images The Glee and Shadowhunters star played Yûki — the host of a competing web show — in the "iGo to Japan" episode of iCarly. He also briefly appeared in the "Trading Places" episode of Zoey 101 as a waiter at Sushi Rox. 12. Jane Lynch (iCarly) Nickelodeon Productions, Presley Ann / Getty Images Jane Lynch, who also starred in Glee, made an appearance on iCarly as Sam's mom Pam Puckett in the "iSam's Mom" episode. 13. Emma Stone (iCarly) Nickelodeon Productions, Mark Ralston / Getty Images The La La Land star played Heather — a huge fan of Carly and the gang — in the "iFind Spencer Friends" episode of iCarly. 14. Mark Hamill (SpongeBob SquarePants) United Plankton Pictures, Michael Tullberg / Getty Images Star Wars star Mark Hamill voiced Mermaid Man's arch nemesis, the Moth, in four episodes of SpongeBob SquarePants. He first appears in the 2007 episode "Night Light." 15. Jim Parsons (iCarly) Nickelodeon Productions, Handout / Getty Images Jim Parsons, who you might recognize from Big Bang Theory, guest starred in the "iLost My Mind" episode of iCarly as Caleb, who tried to convince Gibby he was from the year 2077 and needed to get back. 16. Alex Trebek (Rugrats) Nicktoons Productions, Amanda Edwards / Getty Images Beloved Jeopardy host Alex Trebek voiced Alan Quebec — the host of the fictional game show "Super Stumpers" — on Rugrats. He appeared in the 1993 "Game Show Didi/Toys in the Attic" episode. 17. Johnny Depp (SpongeBob SquarePants) United Plankton Pictures, Loic Venance / Getty Images Johnny Depp voiced the surfing legend Jack Kahuna Laguna in the 2011 episode of SpongeBob SquarePants called "SpongeBob SquarePants vs. The Big One." Jack helped SpongeBob and the crew get back to Bikini Bottom after they get pulled away to a distant island by a big wave. 18. Ke$ha (Victorious) Nickelodeon Productions, Kevin Winter / Getty Images Kesha appears as herself in the "Ice Cream For Ke$ha" episode of Victorious, where the gang tried to win a private concert by finding the letters that spell out "KE$HA" inside ice cream tubs. Kesha's little brother also made a cameo in the episode, as the little boy who found the last letter. 19. Jimmy Fallon and Tina Fey (iCarly) Nickelodeon Productions, Michael Loccisano / Getty Images Jimmy Fallon and Tina Fey appeared as themselves in the "iShock America" episode of iCarly, in which they invited Carly and her friends to be on an episode of Late Night. 20. And finally, David Bowie (SpongeBob SquarePants) United Plankton Pictures, Hulton Archive / Getty Images David Bowie voiced the Lord Royal Highness in the SpongeBob SquarePants musical special episode "Atlantis SquarePantis" in 2007.