There's a 36 second montage of footage from the entire series on Disc 6, called "The Gift". Starts slowly then builds to blinding speed. There's actually a lot there so get ready with the slow motion button. Here's how to access it...
Insert Disc 6 and enter the "Special Features" area.
Select Featurettes and press your Enter button to get into that menu.
Select any of the featurettes and press your Left button button to highlight Buffy's signature "B".
Press your Enter button and away you go but hold on tight as it's a fast ride.
Insert disc two. Go to Once more with feeling. Go to language menu. Highlight resume episode and press your Up button to highlight a B. Press your Enter button. Here you will find a little something about an autograph signing for once more with feeling episode.
Insert disc 4. Go to Doublemeat Palace. Go to language menu. Highlight resume episode and press your Up button to highlight a B. press your Enter button to find out how to access a call sheet for the episode normal again.
All easter eggs were generously submitted by SirDonk