If there is absolutely no need for a device to be USB powered or enabled, you can almost guarantee that Thanko will have it for you. Case in point: the USB Soldering Iron. Should your electronics work space has spilled over into your computer room, this USB powered soldering iron may give you some other options or at least some more convenience.
This soldering iron should be able to handle light soldering tasks with its 3 power options. You can use any standard USB cables, but you will only be able to get about 300 degrees out of it. Opt for the included dual connector USB cords, and you can push that up to 350 degrees. That should get you hot enough to be able to work with highly lead based solder.
Conveniently, they include a 3rd rather scary power option. U sing their 9V to mini-USB connector you can jump the all the way up to 450 degrees. This should get you, just barely, able to work with most commercial soldering compounds. That is, unfortunately, for only as long as the 9V battery lasts. 9V batteries do not have a great track record for being long lasting under high drain applications. If you just have to have something that might almost, just barely, be able to do what you are asking, it should only cost you around $30.