I have a second grader who really hates writing. At his teacher's suggestion, we've started an activity this year that is really helping. We have a spiral notebook for him and we're using it to keep a journal together. He has to write in it for 20 minutes each week (he can either break it up into 5 really short entries or do a few longer ones - as long as he's actually moving his pencil on the paper for a total of 20 minutes a week).
The only requirement for the journal writing is that he has to ask at least one question in each entry. We don't worry about his spelling or even his sentence structure. As long as we can read it and figure out what he's saying it's fine.
Every time he writes an entry, his dad or I write back. We comment on what he wrote, answer his question(s), and ask him one or more questions.
In his next entry, he answers our questions and writes some more of his own. It can be as simple as "What are we having for dinner tonight? I hope it's mac and cheese!" or it can be something deeper like "Who was your best friend when you were little?"
We turn the journal in to his teacher each Friday and she writes a few comments but mostly just puts a star next to each entry to encourage him.
I can't say there's NO complaining about the exercise but it's helping him a lot and I think he's actually having fun with it (although he'll never admit it! ;-)