Denny's is an American table service diner-style restaurant chain. It operates over 1,600 restaurants worldwide and is now known for always being open and serving breakfast, lunch, and dinner around the clock.
In "Road to Europe", after Lois embarrasses herself and Peter at KISS Stock, they find KISS having breakfast at Denny's where Peter finds that she once had a relationship with Gene Simmons, redeeming her in his eyes.
Brian has to deal with a screaming baby at Denny's in "Screwed the Pooch".
Peter compares New Brian's pancakes favorably to IHOP, Applebee's and Denny's in "The Man with Two Brians".
In "The Peanut Butter Kid", Peter declares that Stewie is happier as the peanut butter kid than a sunny-side up egg. A cutaway show an egg on a frying pan saying it's a great way to start the day, until he realize he's at Denny's and that he guy who's about to order him is only gonna eat the toast and put a cigarette out on him.
While pretending to call plays during a backyard football game in "Bri-Da", Joe points out that Peter's play sheet is really a Denny's menu. Peter brushes this off but the play he calls is 'Moons over My Hammy.'
When recounting his tale of being a tennis star in "Tales of Former Sports Glory", Quagmire dreams of winning the Grand Slam, which turns out to be the Grand Slam breakfast at Denny's.