If you own an android device and want to purchase applications AppSales can help you to find applications whose prices are dropped (may be for a short time). This is really a cool website, and it also have an android application too.
You can either check it on the website here - http://www.app-sales.net/
or
Can download the android application from the Google Play Store
Note: Due to the fact that publishers can set different prices for each country, it might happen that the price in your country is not dropped.