Mad Men is known for its retro references, but the premiere of season seven  had us feeling nostalgic for a different era: the '90s. Neve Campbell, famous for Scream and Party of Five, popped up as a potential love interest for Don Draper. She's not the first actor familiar to many of us millennials from our childhood to get a part on AMC's 1960s period drama. Show creator Matthew Weiner recently shed light on the casting, telling the New York Times , "I want to give people the chance to be seen in a new light." And indeed he does. Since guest appearance are never announced by the network, the surprise cameos have definitely become a fun part of watching, and some have turned into more regular roles. Let's take a look our favorites.
On Mad Men: Since season one, O'Connor has had a recurring role on Mad Men as Trudy Campbell's father and Pete Campbell's father-in-law, Tom Vogel. At first, his relationship with Pete was beneficial for the budding accounts man. Tom helps finance their apartment and also gives Pete the Clearasil  account. But once Sterling Cooper Draper Pryce decides to go for the Ponds account, Pete has to drop Clearasil and things get ugly. Making things even more strained, later Pete and Tom run in to each other at a brothel.
Where you recognize him from: O'Connor played Marshall Darling on Nickelodeon's Clarissa Explains It All. As the hippie-turned-architect father of the family, you'll recall Marshall always calls Clarissa "sport" and never really manages to offer her good advice.
Source: Nickelodeon 
On Mad Men: Oleynik plays Ken Cosgrove's wife, Cynthia. Just like Pete's wife, she has a strategic family connection. Her father is CEO of Corning. Ken, unlike Pete, however, avoids relying on her connections.
Where you recognize her from: You know Oleynik as the main character on Nickelodeon's The Secret World of Alex Mack. Remember that impressive ability to morph into a puddle of liquid?
Source: Nickelodeon 
On Mad Men: She plays a widow who lost her husband to alcoholism and then finds herself sitting next to Don Draper on a red eye from LA to New York. When she propositions Don, he turns her down. Although he does accept her cuddles.
Where you recognize her from: Neve was the star of Scream and also appeared in six seasons of Fox's Party of Five as the older sister struggling to provide for her orphaned siblings.
On Mad Men: As Sylvia Rosen, Cardellini becomes Don Draper's mistress and object of obsession. The Rosens live in the same building as Don and Megan, and when Sylvia tries to break off their affair — an affair Sally witnesses, by the way — Don goes in a downward spiral.
Where you recognize her from: Cardellini played Lindsay Weir on the cult hit Freaks and Geeks.
On Mad Men: Bledel's character Beth Dawes starts up an affair with Pete Campbell after meeting him at the train station. But when she undergoes electroshock therapy, she forgets their relationship. Fun fact: Bledel and Vincent Kartheiser, who plays Pete, are together in real life now.
Where you recognize her from: Alexis is best known as Rory Gilmore on Gilmore Girls.
On Mad Men: Marley plays Mary Kay girl Kate, Joan's longtime friend who comes into town and gets Joan to have a little fun.
Where you recognize her from: Remember the hot lifeguard in The Sandlot? That was her!
On Mad Men: McGinley had a guest role as Mel, the head writer on Megan's soap, but you probably remember the character more as the swinger who propositioned the Drapers.
Where you recognize him from: Actually, you probably don't recognize him. But McGinley was Jefferson, the neighbor, on Married With Children!
On Mad Men: Dennis plays Phil Beachum, the Cool Whip executive who is none too impressed with a pitch from Peggy.
Where you recognize him from: As Mr. Belding of course! He was the principal on Saved by the Bell.