I am the queen of substitute curse words, because I don't actually curse. *laughs*
A few of my substitutes:
"Mibs!" *thats my fav LOL
"Sufferin' succotash" (Yes, I do say this ^_^)
"Shimata!" (Japanese for, oh dear, shoot...)
"Freakin freak freak"
"Wha' the frap?!"
"Motor scooter!" (or Motor scootin, if I'm describing something)
...those are just the few I can think of off of the top of my head LOL
My actual "favorite" words: in English, Recalcitrant. Japanese, Kurikaeshimasu ("repeat", I just like the way it flows
) French, erre (the letter R).