API for converting currency such as Euro/USD to BTC Basically what I'm looking for is a reliable API that allows for the conversion of an imputed currency amount such as USD/Euro amount and a conversion would be made that would  convert the amount to BTC.

I want to also point out that I am not looking to convert hard cash for actual bitcoin. I am only looking to determine the current value conversion of a particular USD/Euro at that particular time period. 

I am hoping to use this feature on a current website (HTML/PHP/ETC..) that I am working on.

If anyone can point me to a reliable API that can perform such a task please let me know. Also if you happen to have any guides in regards to implementing/using the API that would also be greatly appreciated.



EDIT:

I want to also point out that I have gathered a few API URLs from numerous websites which can be viewed at the comment section. Now my question is how do I go about choosing the most efficient API and is their any step to step guides, that guides someone in implementing a particular API?
See bitcoin-prices.js library for JavaScript (front end, no server-side components needed) that uses free bitcoinaverage.com API.