after the pearl-clutchiness of the 'c-word' thread, let's lighten it up a little shall we?
My personal faves are:
Fuckingjesus - as all one word, good amount of emphasis there.
Fucksake - would probably be my most frequently used.
Jesus, Mary and Joseph - not a swear but blasphemy, does it count? I like this one as it requires a bit of dedication in time spent.