There is no intrinsic value, but there is a consensus that it has value. That's why you'd like me to send you some. If no one else wanted it, you would not either.
Now a nice flashlight,,,, that has intrinsic value. You know you'd want one even if the rest of your family thinks you have enough.
Daniel
What Daniel is referring to here (please correct me if I'm wrong, Dan) are the conditions necessary for a medium of exchange of any type to exist, whether it be rice, currency, electronic credits, gold, oil, spices, flashlights, whatever. As Daniel pointed out and is shown by history, there is no one kind of valid money - all that is required for a functional medium of exchange is that there exists a some method of transferring ownership of whatever the medium, and that it is accepted by those exchanging goods or services. That's all - not much is required for a functional medium of exchange. In this, Daniel is uncontestably correct - it is such a fundemental truth that this information could be derived from observations of a barter economy that existed without "money."
The key is that not all mediums have the same qualities of scarcity, durability, etc. Until the era of currency arrived, mediums of exchange tended to be those items which were universally desired like spices, foodstuffs, timber, oil, gold, land, etc. These were all available in finite amounts and produced by many people in many places. They were commodities, and as such were a secure store of value (excepting food, which is so universally desirable that its transient nature is unimportant) which could not easily vary in purchasing power.
This begs the question: What functions/qualities should the ideal money fulfill?
1) Money should be first and foremost a medium of exchange.
2) Money should have a relatively stable (over a meaningful span of years) value, meaning that the amount available in the economy should not fluctuate to any great degree.
3) The value of money should not be subject to the whim of any person, group, organization, etc.
4) Money needs to have a practical value-density - meaning that if you try to use something too valuable for money, you'll have a hard time buying small things (try cutting a diamond small enough to buy a Coke) - but if the value-density is too low (like sand, for instance) then you'll have trouble buying anything at all - there needs to exist a happy medium.
5) Money should be durable, so that ideally, one would use money as currency.
If any money meets those criteria (I may forgotten something, please point out anything I'm missing) then it will be almost immune to inflation (I say almost because the Gold Rushes in the US caused a few small hiccups), the government of a society using such a monetary system would be unable to function on a deficit, and encourage financial responsibility. Incidentally, this tends to seriously reduce or eliminate military action except with the direct, voluntary financial support of the People. Based on this, how many think Vietnam would've lasted half as long, or even occurred? How about the First Gulf War? The current mess in Afghanistan? Iraq? Military action would essentially be resistricted to defensive action - as it should be.
This is all to say that Daniel is correct - our currency as it is today functions as a medium of exchange because it is desired and accepted by others, and anything may be used as a medium of exchange if it is accepted. My point is that while anything can be used as a medium of exchange, only certain things SHOULD be used as a medium of exchange.