I haven't yet seen the episodes with all the deaths mentioned here, but I do know about them all. Just hearing that they die, or seeing clips in fan music videos, is shocking and upsetting enough for me.
- Angel. It still kills me to watch it.
- Buffy. When she needs to stop the portal from opening in place of Dawn.
- Doyle. Loved the character, he was actually one of my favorites for a while.
- Jenny. She wasn't particularly a favorite of mine, but I love Giles, and I couldn't believe that Joss killed her off... I just felt so freakin' bad for Giles.
Deaths that I know about but haven't fully seen are Joyce, Anya, Tara, and Cordy. I'd imagine that I'd be most upset over Joyce and Tara. Both causes of both deaths just send shivers down my spine - it's not just some demon, it's... real.