It strikes me that there's a singular lack of crossover vids, taking in two or more fandoms, which seems odd since sometimes the genres, lighting, etc. are close enough together that it ought to be possible to combine frames and make an interesting film. This ought to become easier as the editing technology improves. A few possibilities for crossovers:
Max (Dark Angel) and Faith (BtVS / Angel)
Giles (BtVS) and John Steed (the Avengers)
Willow (BtVS) and PsiCorps (Babylon 5)
Stargate and Men in Black
Buffy / Angel & Highlander sword fights
Farscape & Angel (especially Caritas)
Faith (BtVS / Angel) and any of the Farscape women
Some sort of sword dancing / meditation thing with Buffy / Angel / Cordelia / Highlander people / etc.
Unfortunately I have no talents in this direction at all, but it'd be nice if anyone who does know of videos like this comments with a pointer.