There are plenty of productivity apps available for Android. However, the problem is that most of them are quite expensive. For example, one of the better ones is Docs 2 Go, but it costs £9.99 for the full version. Now Google has stepped in to fill the void with a free app that's essentially a phone interface for its cloud based Google Docs service.
It allows you to view and edit documents and once you're done making changes you can save the results to Google Docs's online storage. The app still needs quite a bit of work, especially on its tablet interface, but it's slowly getting here. There are some neat new features appearing, including one that converts pictures into documents, complete with OCR'd text.
It's far from perfect, especially as the tablet interface is poor. However, for use on phones, Google Docs is a good free alternative to pricey paid for productivity apps.