I like Handwriting Without Tears. It's been great for my ds with fine motor issues and also for my girls who have fairly advanced fine motor skills. You can see sample pages on their web site.

Other ideas for strengthening the small muscles used for writing: painting with brushes, sponges, cut up potatoes, etc.
playing with hard clay (playdough is too soft to do much good)
modeling with beeswax
tearing up newspaper, wadding it into balls
lacing cards


hth!

Lorel