If you're happy working in C/C++ then the Marmalade SDK is a good option. It lets you write a single code base that can then target iOS, Android and BlackBerry (certainly Playbook and I believe BB10 too, or at least soon). Windows Phone 8 support has also been promised to arrive shortly.
Note that it isn't free however (although a free trial is available).
Check out http://www.madewithmarmalade.com for more information and if you think it looks like it will suit your needs then (shameless plug alert!) you could also pick up a copy of the book I wrote that shows you how to get to grips with Marmalade - http://www.packtpub.com/marmalade-sdk-mobile-game-development-essentials/book