The Escapers (makers of Flux, Stuf and more) have an interesting new task management service called Instruktion. Or maybe it's called "New York Minute", it's not clear to me. It is cross platform and the apps are free. It requires a $20/year membership which sounds like a good price.
It looks very nice on all of the application platforms and works offline too. I'm an OmniFocus user but I'll keep an eye on how this evolves.