Provide a link or two as examples so people can quickly try it out. Make it clickable rather than something they have to copy and paste. Maybe have a grid of popular products for this. This allows people to try your service and also gives them ideas of the types of products they might track.

I could see something like this being a really quick way to get alerts when a competitor changes their price. Not sure if there would be legal issues in promoting this though.

In the text here ("Enter your email in the field above for future price notifications"), the field is below, not above. At least, it is in my browser.