Are there any apps for writing/journaling that allow you to "tag" your entries like MeFi allows you to tag your posts? I'm interested in something that lets me write short entries, but also lets me choose, say, from a variety of topics in a tag listing, and then at a later point see my entries by day OR by tag.
I have an iPhone, but for something like this, I'd download it on a dead Android with wifi or a Kindle if I had to.