If you start using Ookong, you'll be amazed how much the prices on Amazon fluctuate for many items and you will definitely be able to save quite a bit of money by purchasing when an item hits a low point. Simple, unobtrusive, and effective. Don't shop without it!
I do find Ookong very useful as I shop Amazon.com quite often for DVD and Blu-ray titles, as well as occasional home electronic items.
Ookong is fully integrated into Amazon.com. When you are shopping on Amazon.com, you'll find a 
button on the item page (See screen shots below). Click it to follow its price updates and view the price history in your Following List.
All your items are saved locally in a place called Following List. You can visit it through the menu bar: Tools -> Ookong or you can click on the Ookong icon at bottom right of your Firefox, select Following List.
When the price drops, you will get a notification from the bottom right of the window. You can change the alert threshold in the Settings (click Ookong icon at bottom right, select Settings)
Another cool feature in Ookong 1.3 is the built-in search engine. Search your favorites in the search box of "Following List", then compare the results directly. Move the mouse over the icon in history column, you'll see their price history charts.
Using Ookong will change your way of shopping. You can find YOUR OWN deals for DVD, GPS, cameras, toys, laptops, mp3 players, video games, and everything. It is easy.
