I have a migraine, so while I was lying down in a dark room waiting for the meds to kick in, I came up with a list of my favorite Giles moments. In no particular order:
• demon Giles in "A New Man"
• "Do you like my mask? Isn't it pretty? It raises the dead."
• all of "Band Candy"
• cleaning Buffy's wounds in "Helpless" while head watcher guy says "You have a father's love for the child"
• "Wish I Could Stay" in OMWF
• that tiny scene of Giles drinking and listening to Cream after Joyce died
• "If it's guilt you're looking for, Buffy, I'm not your man. All you will get from me is my support... and my respect."
• skewering the mayor (with a type of sword I can't remember)
• "I'd like to test that theory"
• the flaming baseball bat of vengeance (my personal favorite)
I could probably list about 20 more, but those are my favorites.