Jeff Garlin, for example, appears as a radio host in the episode "K-GAS". You may also recognize someone from Saved by the Bell and Showgirls amongst the cast during the start of syndicated Season 2 as well.
John O'Hurley, perhaps best known as J. Peterman on Seinfeld and the host of Family Feud from 2006-2010, plays a mentally disturbed man who is convinced his daughter is drowning in "Red Wind". In the same episode, famous talk show and news personality Geraldo Rivera guest stars as a guy who keeps picking a fight with Mitch because he thinks Mitch is trying to steal his wife.
The Other Darrin: Hobie was first played by Brandon Call on the NBC episodes, then later by Jeremy Jackson in syndication.
The character of Neely Capshaw was played by three different actresses, believe it or not. The most famous one was Gena Lee Nolin, who portrayed her from syndicated seasons 6 to 8. But she was also played by Heather Campbell in her debut appearance, syndicated season 5's finale, "Wet and Wild". In syndicated season 9, Nolin was replaced by Jennifer Campbell.