Sounds are pretty cool to use on any website, as long as you don't go crazy with them.  A good place to see sounds put to good you is the Sounds of the Slayer.  An excellent site where they may let you use some sounds if you ask nicely. =)

Images are vital to most websites and especially Buffy sites.  They make the site come alive and look better.  You can get tons of screen caps for your own use at Sunnydale Highschool.  This too is an excellent site.