George Harrison was a big fan of the Austin Powers franchise. The very last letter he wrote was to Mike Myers, praising him for his work. The letter was never mailed to Myers, but coincidentally, it ended up in his hands the day Harrison died. Prior to that moment, Myers had never met Harrison in person, and he cried when he received the letter, which is now framed in his home.
Mike Myers has said that his glasses in all three movies are meant to look like those worn by Sir Michael Caine in Ipcress - streng geheim (1965), so Caine took the original glasses (model "Teviot 74" by U.K. Optical) to the set, and wore them as Nigel.
The items on Austin Powers' briefly-glimpsed "Things To Do Before I Die" list are, in order: Become International Man of Mystery; Save World from Certain Doom; Find True Love; Go to Outer Space; Travel Through Time, Backward and Forward; Be Cryogenically Frozen; Catch Dr. Evil in the First Act; Threesome with Japanese Twins; Win Daddy's Respect.
Mike Myers: [playing multiple roles] Myers played four characters in this movie: Austin Powers, Dr. Evil, Fat Bastard, and Johann Van der Schmutt (Goldmember).
Quincy Jones: During the opening credits. He composed "Soul Bossa Nova", which the franchise used as the theme music.
Susanna Hoffs: In the beginning of this movie when Austin is in his shag pad singing, director Jay Roach's wife and former The Bangles lead singer can be seen playing the guitar to Austin's left.
Kristen Johnston: Who had played Ivana Humpalot in Austin Powers - Spion in geheimer Missionarsstellung (1999), is reportedly one of the dancers in Austin's pad.
Katie Couric: As the prison guard who stands behind Mindy Sterling's character Frau Farbissina when she visits Mike Myers' character Dr. Evil in prison. When Couric was co-anchoring Today (1952), she showed how they FX'd the unibrow on her face, then showed her "Time's Up" line.