For those of you who prefer Sennheiser to RODE, these are a great price too.
If you already have a mic you can just get the $299 set. There is also an XLR version for the same price which lets you plug the transmitter directly into a dynamic mic, news-reporter style.
The receiver sits on your camera's hotshoe and plugs into the mic input on your camera.
Having just one button makes it very quick and easy to set up and use.
If you need a lav mic, the version with the ME2-II mic is only $40 more. The mic itself sells for $105 normally.
The model without the mic is US$299.95 at B&H.
The ME2-II bundle is US$349.95 at B&H.