The show has an impressive number of well known guest characters.
But I still found it fascinating to see Michelle Trachtenberg (Dawn in Buffy) make an appearance (2x16) shortly after Tom Lenk (Andrew in Buffy / 2x06) and Adam Busch (Warren / 2x14).
And btw Michelle's mother is Mel Harris (Oma Desala in Stargate SG-1).