I use a combination of programs including IEW (Institute for Excellence in Writing) and Michael Clay Thompson's language arts program from Royal Fireworks Press. My daughter loves MCT, he combines vocabulary, grammar, literature, writing, and poetry in a fantastic way. We have gone through several levels of his work and I have found that they are very easy to go both wide and deep. We've actually completed some levels, and then gone back and done the writing elements again. For example, last year we completed his Town level program which is for 4/5 graders. This year we focused on the thought organization skills taught by IEW, then went back and did the writing exercises from MCT again. I varied the specifics of the assignments a little so she wouldn't feel like she was repeating, but it has been worth it.
I like the two together since IEW helps teach the students how to take notes and learn the details of structure, but MCT is wonderfully creative and really asks a lot of the student in a way that truly engages them. Both programs cover elementary and middle school.
A third program I have used with mixed success is Classical Writing. If you need a program that leaves little to chance and spells everything out very clearly for you as the teacher, this might be a good option. I like the philosophy behind this program, but my kids have found it somewhat boring and repetitive. It might be more useful used in concert with some of the other programs mentioned.