We see the Borg Queen holding the head of a Borg drone she is examining. The head is actually a model of Brent Spiner's head; it was first used in Time's Arrow (1992) to represent Data's disembodied head.
This episode introduces the class IV tactical Borg cube. It's heavily armed and has multiregenerative security grids protecting its central plexus.
Janeway's line about having a headache last time she heard the words "my mind to your mind" is likely a reference to the episode Flashback (1996).
Susanna Thompson has played four characters in the Star Trek franchise - the Borg Queen in Dark Frontier (1999), Unimatrix Zero (2000), Unimatrix Zero Part II (2000), Dr. Lenara Kahn in Rejoined (1995), Varel on The Next Phase (1992), and Java on Frame of Mind (1993).
Mark Deakins (Axum) also played Tournel in Star Trek: Insurrection (1998), and Turanj, a Hirogen hunter, in The Killing Game (1998).