What is the correct form when we have a rate for each currency in a list of currencies. For example if currencies are EUR, GBP and USD there will be a rate (buy and sell) for each one of these currencies.
"Currency rates" is the preferred form. Personally, I would say that it is the only correct form, but Google does return about 15,000 hits for "currencies rates" (vs. 1,600,000 hits for "currency rates").
Edit: seeing that your question is tagged "British English", I searched the British National Corpus (BNC) and got the following results:
Also, as Noldorin suggests in his answer, there is the more popular term "exchange rate", for which Google returns 12,400,000 hits and BNC offers the following stats:
And, for the sake of completeness:
The usual term is exchange rate. If you want to be unambiguous, say foreign exchange rate.