Windows Phone
iOS
Chrome
Android
Mobile Web
BlackBerry
Samsung
Top 10 platforms currently being used by developers (2012) irrespective of their main platform.
Mobile Web, despite its issues with mobile browser fragmentation it is still being
widely used by developers as it provides a low-barrier, cross platform entry point into the mobile application development. Mobile Web trails behind native development platforms in relation to its APIs but provides a good alternative when cross-platform is plays an important role to the developers app.User expectations are always set by native platforms, therefore native applications will be one step ahead in terms of speed, optimisation and advancements in technology.
Windows Phone is looking to be the next big development platform with the majority of existing iOS and Android developers opting to adopt Windows Phone alongside their standard iOS/Android versions. For development of applications for Windows Phone, you will require a Windows PC, which presents a barrier to entry for iOS developers (and other developers working from the Mac OS X platform.
Blackberry appears to be being abandoned by the majority of developers when compared with other major platforms. Blackberry appears to bring in more revenue on average than iOS and Android, and developer costs for the platform are significantly lower. It is estimated the development cost of a BlackBerry app costs around $15,000 while Android and iOS costs around $25,000.