Building where Father Peter Westley has his offices in episode 4x04 "The Devil Is in the Details… And the Upstairs Bedroom".
Nina and Izzy talk about their clients while walking to class in episode 1x01 "Cigarettes and Funions and Crap". Andy calls Izzy to clarify their situation in episode 1x02 "Can You Be Cool?". Izzy listens to Nina talking about her professor before bailing to find Andy in episode 1x04 "Check a Box". Appears in 1 more episode.
From episode #109 "Sunday Mornings".
Mel is hanging up posters for the protest when she is greeted by Harry Greenwood, the new head of the department who is replacing her mother in pilot episode. Macy meets with Harry to interrogate him with the truth serum but realizes too late that it isn't working in episode 1x02 "Let This Mother Out". Mel is leaving class at night while in Maggie's body and is kidnapped for a rush party in episode 1x15 "Switches & Stones". Appears in 1 more episode.
Harry is shown a memory from his forgotten past of him robbing a bank and then being arrested in episode 1x10 "Keep Calm and Harry On".