The Undead Templars upon their dead steeds riding in slo-mo in
Tombs of the Blind Dead. Still give me the chills now, especially with that soundtrack. Love it!
Oh & when the zombie wanders into the house in
Shaun of the Dead & surprises Simon Pegg & Nick Frost on the sofa.
'Ohh, for God’s sake! He’s got an arm off!' 
Worst scenes? Probably the whole of
Platoon of the Dead. Never get that time back, what a stinker!