I see many variations of spot prices from site to site. What site or sites display the actual bid/ask spot prices in real time?
There are as many spot prices as there are markets (i.e. lots). They're all pretty close to one another because when prices diverge, people can buy low in one market and sell high in another market. Enough people do that for there to be lots of competition and hence a very narrow margin, but there will always be small differences in prices published by different parties.