Making money on the trading post depends a good deal upon having historical data to see the trends in item pricing. GW2TP.com is a site that is designed to help us, the end user, see those trends.
At first glance the site shows just a couple graphs and not much else. If you scroll to the bottom of the page you’ll find the current gold to gem conversion information as well as a breakdown of how much real-world money it costs to buy 1 gold. The true beauty of this site those is in the historical data for individual items.
Here is a screenshot from the current items page:
From this you can see that Copper Ore is selling for 22c per, and the current offers are at 18c. You can also search for any item in the game and get the same statistics.
Clicking on the item will bring up the historical trends in a nice, neat, graph tracking the historical data. Check out the site at gw2tp.com and let the speculation begin!