hvala za...

Dear Namoru, it is completely wrong to say ''Hvala za''. You would absolutely want to say ''hvala na vašoj pomoći'' if you want to say ''thanks for your help''. ''Hvala za'' is said a lot though, but only by those not knowing standard language rules! I am really sorry people are giving inaccurate advice. Regards, d.

You're welcome! :) If you have any questions, feel free to ask.

Velika hvala Morana! Your explanation made the point clear. I'll try to read a lot and use both expressions to understand the nuance...

You can use both expressions. The difference is in grammatical case of the word (whatever you are thanking for). The preposition "na" in this situation is followed with a word (or words) in locative. And the preposition "za" goes with accusative case. I'll give examples for both expressions with the same word. Hvala na savjetu. Hvala za savjet. Meaning: "Thank you for advice." Sometimes both ways are equally common to hear with a particular word or expression, and sometimes one way is more common than the other. But unfortunately I can't really help you with that in general, because there is no strict rule.