All of these are Buffy-centric and/or "gen" vids that remind me why I love the Buffyverse, and Buffy Summers, so much. The same superlatives applies to each of them: presenting ideas, themes or arcs in the verse in new or unusual ways; excellent editing to the beat, rhythms, mood and lyrics (as applicable) of the music; matching visual movements from one shot to the next. Listed in alphabetical order by the vidder's screenames.
"Buffy the Vampire Slayer Tribute Trailer" by Afterthebattle - Finished in time for International Women's Day 2013. I've seen a lot of so-called "epic btvs vids" but this one truly is epic; set to a remix of Ennio Morricone's "The Ecstasy of Gold".
"It's Not My Time" by MrMorda898 - Another gen tribute trailer from MrMorda but the upbeat title song by 3DoorsDown gives it a very different feel from the other vids on this list.
(One caveat: I'd love to see all vidders remember to include the song credits (title and artist) as the music used is very often new to me.)