'Shit' is 'paska' in Finnish. 'Son of a bitch' would be 'nartun penikka', but no one ever says that, it sounds more like joking than insulting. You can say 'kusipää' ('piss head'), 'vittupää' ('cunt head') or 'paskiainen' ('douchebag') instead.
Let's not forget the everuseful f-word! :) It's 'vittu' in Finnish. You can use it also in a pattern 'f*cking xxx' by saying 'vitun xxx'.
Have a good time swearing in Finnish! ;)