PlayNoEvil is a blog that claims to do "MMO security news and analysis" -- they've got an interesting post up trying their best to track gold selling prices over time in various MMOs (the information itself seems to come from MMOBux.com). The World of Warcraft graphs (US seen above, EU on the site) show that for whatever reason, in the US at least, gold prices seem to be dropping. Of course, whether that's driven by low demand (thanks to Blizzard's daily quest implementation and other anti-gold selling mechanics), or high supply, we aren't quite sure.
In the EU, things aren't so clear -- while there are still bumps around content releases, things are holding pretty steadily at a price well below the United States. Either way, no matter what price it is, we should note as well that buying gold from anywhere is against Blizzard's terms of service and will get you banned. Hopefully, these lower prices in WoW mean that Blizzard's attacks on goldsellers are working, and that low demand has driven the price down further than its been in a long time. Even so, and even assuming that these prices actually do correspond to the market (no idea where MMOBux gets their info from), there's not much concrete info we can suss out of this other than the fact that prices are dropping in the US.