Air Video is great, and it is very similar.
Although, as far as I know Air Video does not allow you to stream music, only video.
I would like airplay to recognise my iPhone or iPad as a speaker, that would be perfect, and im sure Apple are working on it.
There is a jailbreak method of doing this, although im not jailbroken so I couldnt really help you with that im afraid.
But in the mean time Zumocast does it just fine for me.