Freyja may not be mentioned in Beowulf, but her beautiful necklace, Brisingamen, is. Check out necklace mention at line 1199.
Richard Vagner's Der Ring des Nibelungen epic operas about Norse mythology feature a character named Freia, inspired by the goddess Freyja.
Freyja pops ups in the cheesy '80s comedy Erik the Viking.
Freyja appears as a boss in the online role-playing game World of Warcraft.
American heavy metal band The Sword wrote a song about Freyja called "Freya." In the song, Freyja is performing her role as a Valkyrie, selecting dead warriors to go to Valhalla. You can read the lyrics here.