Audio:
Episode 26 contains a secret 4th audio track that is completely silent until the final credits. At that point, Spike Spencer (Shinji's Englsh VA) launches into a hilarious rant about Neon Genesis Evangelion's ending (or lack thereof).
Reported by: Matt Czyz

Bonus Feature:
In the bios section of Evangelion Volume 7, if you hit "Enter" where the Continue button was on the previous bio pages, info about the 17th angel will come up.