I don't use it because I'm on an iPhone, but I know that there is this great app called Todo.txt out there. It's really simple to use.
If you want a more "robust" client, aka one that has more than just a text file, try out wunderlist. I don't use it because I've been using Things for forever and I love it, but in your case, you need an android app. I've heard excellent things about this as well.