Check out Cocos2d-x. It's completely free and open-source.
There is also http://www.appgamekit.com It's something I am interested in. It supports "Basic" as well as "C++".
I think that Marmalade is really powerful. I've messed around with it. And highly recommend it.
If you are only targeting Android and iOS for a 2D game, I would highly recommend Cocos2d-x. It's one of the most game-complete and free framework for C++ I've come across.
The advantage of using Cocos2d-x opposed to Marmalade is that most of the components of a game engine is written. You can prototype a game in less than a day. Cocos2d-x is also free.
I wrote my own game engine with Marmalade and it took no longer than a week (on and off work, of course).
The disadvantage of Cocos2d-x is obviously less variety of platform support.
If you're willing to spend a bit of money but also need the simplicity that Cocos2d-x offers. Check out http://appgamekit.com It's cheaper than Marmalade SDK and easier to use. It is also extensive via C++.
Deciding on what to use mainly depends on your constraints. I am currently using Cocos2d-x for an upcoming project scheduled to be released for iOS very soon.
