Yes, Woodstock was named after the 1969 music festival.
Peppermint Patty was named after York Peppermint Pattie candy.
One strip featured a shout-out to MAD magazine and Alfred E. Neuman.
In turn, MAD had done a bit about the Peanuts gang as teens and adults. Schulz wrote in and said, "Why don't I retire and let you guys take over?" It was signed with a sketch of Snoopy saying, "What, me worry?"
A 1961 strip has Linus telling Lucy that he filled out a personal information card for school. When asked for the name of his family physician, he didn't know, so he put down Dr. Seuss.
The 1984 special It's Flashbeagle, Charlie Brown contains a sequence during the otherwise original song, "I'm in Shape", where Peppermint Patty sings a bridge that clearly is a spoof of Toni Basil's hit "Mickey".
That whole special is a shout-out to various elements of '80s pop culture. The "Flashbeagle" theme song itself obviously spoofs "Maniac" by Michael Sembello.
1950s songbird Joni James is mentioned in one strip as one of Snoopy's favorite singers (he tells the Cat Next Door not to bother asking to borrow any of his Joni James albums ever again), and in a Sunday strip in 1989 in which Linus is unable to use the telephone for a phone-in contest in which the prize is four tickets to a Joni James concert - because Lucy is hogging the phone. James returned the favor by including Snoopy on the cover of her compilation CD Jukebox Joni.
Frieda's cat Faron was named after country singer Faron Young.
A fairly obscure one is Charlie Brown's favorite breakfast cereal, "Snicker Snacks".
Quite a few to Billie Jean King. In one strip, Sally draws a picture of George Washington and Betsy Ross playing a mixed doubles match against Harry Truman and Billie Jean King for Independence Day. Charlie Brown comments that Harry and Billie would have won in straight sets.note King was a close friend of Schulz and even spoke at his funeral.
One Sunday comic in the mid-1990s shows Snoopy about to participate in a hockey game with Woodstock and several other birds. Snoopy was surprised to find out that before every game, they do the Macarena.
Here's one from a 1980 strip involving Peppermint Patty's feet wrapped in comic book pages. The character isn't much of a surprise, receiving shout-outs all the time from one place or another...
In a 1999 strip, Sally writes a fan letter to Harry Potter. She is visibly disappointed when Charlie Brown tells her that Harry Potter is not a real person.
The Great Gatsby got lots of Shout Outs in the last decade or so of the strip. Schulz apparently became very interested in the work of F. Scott Fitzgerald in his later years, spurred on by the fact that he and Fitzgerald shared St. Paul, Minnesota as a hometown.