I never used the level editor myself, but Robot Wants Kitty is a great Metroidvania-style game which has a level editor. There may be a 69p IAP to buy the editor, although I don't remember for sure, but it's a free download so there's nothing to lose.
Zombie Tales FPS Creator I just released a game called Zombie Tales for iPhone and iPad. You can create simple FPS maps. It's more level editor than game. I'd be keen to see what people think?? It's free till the end of November. http://itunes.apple.com/app/id592562865 It works best on iphone 5 / ipad 2 and above and I'm still refining it. I've got a couple vids at YouTube.com/zombietalesgame Cheers