Question: What is the most reliable and up-to-date source for getting world currency exchange rates?

Answer: 
I consider [Reuters](http://www.reuters.com/finance/currencies) to be THE source.
Forex rates are universal. Most of the website provide you with almost the same exchange rates with a margin of +/- 5 pips which is usually due to different spreads provided by different institutions or server delay.

Check out:

www.netdania.com
www.xe.com
www.fxstreet.com
www.dailyfx.com

I personally use netdania's application on my iPhone