Cocos2D is the most popular 2D iPhone game framework. An alternative, if you're used to the Flash/ActionScript way of doing things, is Sparrow. You may also find that if you're doing an action/physics game in the future, Box2D will inevitably be necessary.
If you're looking for a GUI as opposed to a programming API, in addition to the fine options above, my startup (http://www.stencyl.com) also does this and is based on Sparrow (and Flash for exporting to the web).
However, I'll be realistic and say that if you're making an RPG, you'll find it much easier to build it by hand.
Thanks! The Balls in Space game scored several sponsorships that have collectively gotten it into the 4 figures range, which is pretty good by Flash standards.
If you're looking for a GUI as opposed to a programming API, in addition to the fine options above, my startup (http://www.stencyl.com) also does this and is based on Sparrow (and Flash for exporting to the web).
However, I'll be realistic and say that if you're making an RPG, you'll find it much easier to build it by hand.