According to new reports published earlier this week by Citibank and Gartner, the App Store should bring in at least $2 billion in revenue in 2011, about half of an overall apps market estimated to be over $4 billion by the end of the year. Between the upcoming iPad 2, the alleged Verizon iPhone 4, and a potential iPhone 5, the iOS eco-system should grow substantially in 2011, and Apple should be able to add dozens of millions of app hungry new customers to the pool of hundreds of millions of existing iOS users. While these numbers are already quite impressive, analysts believe the market will literally explode over the next three years, as the overall apps market is expected to bring in over $27 billion in revenue by the end of 2013 – a staggering seven-fold growth over the next couple of years. Apple started the app revolution back in 2008 by launching the App Store, the most successful mobile applications marketplace ever built. In less than three years, the market grew from nothing to a multi-billion dollar business, with dozens of millions of apps downloaded every single month. Between Google’s Android Market, Microsoft’s Windows Marketplace, RIM’s App World, HP’s Palm Catalog, and Apple’s App Store, the next couple of years will be the battleground of an intense war between major players trying to get the largest piece of an ever-growing pie.