The excellent teachingenglish.org.uk site has a new article on Making writing communicative (which it often isn't in a language classroom, particularly when writing is something the learner does, hands in to the teacher… and that's that).
The article mentions blogging, which is one way writing can be made more communicative, particularly if all your learners are writing on a single class blog, and writing comments on each others' work, too. Doing so, and creating something that is shared will also create "tasks that are intellectually satisfying", I would suggest.
Among the books listed in the bibliography at the end of the article is Process Writing (Arndt and White, Longman 1991), one which I can highly recommend. Getting people to write in pairs, or at least to comment on each other's work (whether or not it is via a blog) is one aspect of process writing and — because you talk about what you are writing — another way in which it can be made communicative.
Getting learners to write — and read — stories is another. Some of your learners will no doubt say that they don't like writing, but there's also fun in the process that I think even they will come to share.
Here's a fun story from Ananova.com about fish making a bolt for it from a trout farm that might make the start of a piece of (shared) creative writing. Process writing would require you to brainstorm first, before you start to write: who will the narrator be? One of the characters named in the story? Or one of the trout, perhaps?
And that's where the fun begins…