methods of purchasing apps

i'm not sure this has been covered or not but after searching it came up with nothing, anyway after trying to find free apps i keep finding ones full of adverts not only do i find them annoying (i know they are there for a good reason for developers) they also drain my credit from my prepay account. i know you can turn them off by downloading a controverrsial app and using a rooted phone, but i would rather pay for the full app and get more features, but the one thing that annoys me about purchasing apps through android is you need a credit card, one which i do not have or particularly want to have. is there any global system where you can go out go to store and get credit to use on the android market like apple does on itunes? i find being able to go to the store and buy credit and then spend it as you choose is realy usefull, especially in a society where we have to be seen with particular things. i got an android phone seeing as it as a cheeper alternative to the ios, yet ios is much more accessible for people of all ages.