Bones to Hangin' with Mr Cooper

An episode of Bones has a reference to a prostitute who worked at the (fictional and from the CSI universe) Tangiers hotel.

Morley cigarettes are smoked by Warrick Brown in a episode of Crime Scene Investigation.

Homicide's John Munch questioned The X-Files' The Lone Gunmen.

Homicide's detectives watched Oz's Miss Sally on TV.

St Elsewhere's hospital management company Weigert (was Ecumena) took over Oz's hospital.

The Bob Newhart Show's Elliot Carlin visited the psych ward at St Elsewhere's St Eligius Hospital.

The Bob Newhart Show's Bob Hartley woke up after dreaming the entire series Newhart during Newhart's finale.

Newhart's Larry, Darryl and Darryl squatted in Coach's Hayden and Christine's home

On a network crossover night, The Drew Carey Show, Grace Under Fire's Grace Kelly, Coach's Luther and Ellen's Paige and Spence all show up. Finally on Ellen, Paige and Spence run into Grace Kelly and Drew Carey

The Drew Carey Show's Mimi appeared in an episode of The Hughleys

The Hughleys crossed over with The Parkers.

The Parkers was a spinoff of Moesha

Hakeem and Niecy from Moesha went to the prom with Cher and Sean from Clueless.

Sabrina from Sabrina the Teenage Witch visited Cher from Clueless in the episode "Mr. Wright."

Sabrina the Teenage Witch also crossed over with Boy Meets World on several other occasions.

Boy Meets World and Step by Step both had episodes at Disney World and whiel in Disney World Eric from Boy Meets World met Dana from Step by Step.

The family from Step by Step was in the middle of a barbeque outside when Urkel from Family Matters came (literally) crashing in on the jetpack he had built on the last episode of Family Matters.

Steve Urkel visited Stephanie Tanner of Full House to convince her that glasses could be cool

Michelle Tanner from Full House appeared on an episode of Hangin' With Mr. Cooper in which Mr. Cooper was her substitute teacher.