I love the word "fuck". I loved the scene in The Wire (love The Wire) when cops went into the crime scene house and did their investigative thing only saying "fuck" with a variety of meanings. Such a useful word!
I say "oh god" or "goddamn it" on occasion and I do think that its a little strange that I use it. I think its because its so ingrained into me I just can't shake it. My mother in law says "dogs" often when she wants to curse.
Depends on situation. If it's nothing big I'll say "hell" or "damn", this escalates to "shit" "fuck" "piss" ect ect. If I'm really really pissed I'll yell something like "piss shit bitch!" or my personal favorite "Great Jupiter's COCK!".