Chris calls out Tapjoy as a means to buy your way to the top 25; however, that's not entirely fair, imo. Increasing App Store ranking is a side effect of any promotion/advertising service. While the incentivized nature of Tapjoy brings into question the quality of these acquisitions, it's ultimately a fair and honest method to promote your app.

On the other hand, services like http://appmagenta.com and http://gtekna.com are downright shady. With enough money, you can buy enough fake downloads to reach the #1 spot in the App Store