Lazarus Rising (4x01) - Sam's cell phone is registered under the name Wedge Antillies. Reference to a Star Wars X-Wing fighter pilot, and friend of Luke Skywalker.
Are you there god? It's Me, Dean Winchester (4x02) - None
In the Beginning (4x03) - Dean uses the name Dean Van Halen when he introduces himself to the young John Winchester. Van Halen is one of Dean's favorite rock bands. Dean also introduces Samuel Campbell, his maternal grandfather, as Father Chaney when they visit Mrs. Beth Wiltshire.
Metamorphosis (4x04) - None
Monster Movie (4x05) - FBI Agent Angus (Sam) and Agent Young (Dean). Angus Young is the lead guitarist and founding member of the rock band AC/DC.
Yellow Fever (4x06) - FBI agents Tyler and Perry. Steven Tyler (lead singer) and Joe Perry (lead guitarist and occasional lead singer) are members of the band Aerosmith. Also Tyler Perry is a film Actor, Screenwriter, Theatre director, Film director, Television director, Playwright, Film producer, and Television producer.
It's the Great Pumpkin, Sam Winchester (4x07) - Agent Geddy (Dean) and Agent Lee (Sam). Geddy Lee is also the lead singer of the band Rush. Dean later goes by the alias of FBI Agent Seger. Bob Seger is a rock singer known for performing with the Silver Bullet Band.
Wishful Thinking (4x08) - In this episode the boys go by many aliases. Sam impersonates an author, telling Candice that he is writing a book by the name of Supernatural. Sam and Dean later impersonate FBI Agents investigating a "Big Foot Sighting". When the Winchesters in counter a young girl and her foul mouthed, drunk, Giant Teddy Bear friend they pose as Teddy Bear doctors. They diagnose the bear with Lollipop disease; which is common for bears his size. In order to investigate a Wishing Well located in a Chinese food restaurant; they pretend to be from the Health Department. Later, they impersonate florist for a wedding.
Heaven and Hell (4x10) - None
Family Remains (4x11) - County Code Enforcement Officers Babar (Dean) and Stanwyck (Sam). Babar is the titular character of the children's book "Babar". Both aliases are an homage to the movie "Fletch" (1985). Irwin 'Fletch' Fletcher (Chevy Chase) uses the alias Babar while visiting Dr. Joseph Dolan (M. Emmet Walsh). Alan Stanwyck (Tim Matheson) is the one of the main characters of Fletch's investigation. Alan Stanwyck is also the alias Dean uses in 2x04 Children Shouldn't Play With Dead Things. Their aliases could also be construed as Barbara Stanwyck, the American actress, but it doesn't quite fit their M.O.
Criss Angel is a Douchebag (4x12) - Dean introduces himself as Agent Ulrich. Lars Ulrich is the drummer of Metallica.
After School Special (4x13) - Dean is Truman Highs Coach Roth. David Lee Roth is the lead singer of the rock band Van Halen. Sam poses as a janitor at the same school, but his aliases name is never mentioned.
Sex and Violence (4x14) - FBI Agent Sam Styles and Agent Dean Murdock. Murdock and Styles are from the show Route 66. Which is how Kripke initially described the show.....Route 66 with ghosts!
Death Takes a Holiday (4x15) - Sam and Dean pretend to be bloggers from a website by the name of flooredbythelord.com
On the Head of a Pin (4x16) -
It's a Terrible Life (4x17) - In this episode Dean and Sam aren't pretending to be someone else, but actually are someone else. Dean and Sam Winchester become Dean Smith and Sam Wesson. A tribute to the gun makers Smith and Wesson.
The Monster at the End of This Book (4x18) - Agent DeYoung and Shaw. Dennis DeYoung and Tommy Shaw are members of the rock band Styx.
Jump the Shark (4x19) - Dean used the alias Agent Nugent for the second time in this episode. The pilot episode being the first. Ted Nugent is a hard rock guitarist. First becoming famous as the lead guitarist of the Amboy Dukes.
The Rapture (4x20) -
When the Levee Breaks (4x21) -
Lucifer Rising (4x22) - None