It's my first entry, so excuse my rash contribution.
Well, money is a promise by the issuing bank (or state) to surrender a certain good (usually gold) as soon as the owner claims it. So what makes it valuable is the general value of the promised good and the ability of the issuer to actually give it to you (generally speaking) when you present it to him. On the other hand, it makes transactions much faster and easier because I can simply use money as a substitute for the good itself.
Having said this, I do not see how else this question could be answered. I can't list everything that affects the actual value of paper money, because basically everything can affect the value of money. But let's say your question goes beyond our usual definition of money, I mean not just paper money, but money in a broader sense. Since gold has no intrinsic value and is sought after solely for its exchange value, we could also call it money. However, it is not issued by any bank or a state. So where does the value of gold come from? This seems to me to be a chicken or egg problem.