Buffy and Angel....

One thing I enjoyed about this game was the fact that the characters looked like the actors who played them rather than just having their voices which made it easy to figure out where you knew them from, not always that easy with vocal work.

While I recognized a couple of people from other things (the main guy and a smaller character from Mad Men, the property developer was the Steward of Gondor in TROTK etc.) the bulk of them seemed to be from Buffy/Angel -

The coroner played a demon in Buffy and a stalker in Angel

The Arson Desk partner was Holtz in Angel

One of the cops played Tara's dad in Buffy

The head fireman was Spanky the warlock in Angel

The little old lady was the penis/snake-headed thing in the Doublemeat Palace episode in Buffy.

Angel's son (also in Mad Men) pops up in one scene

Mickey Cohen was in Angel

and there were a few others but I cant remember them off the top of my head.