The Academic Writing Club offers online writing groups for scholars—grad students and faculty. The site also offers a great deal of advice on writing, and the daily log in schedule of the writing club is truly effective at a cost of $70 per month. If you can afford it and you need the discipline, this is a very useful tool. High quality, private coaching is also available through this site.
Marie Deer is a private writing coach who charges $90 per hour for telephone sessions. She is knowledgeable and extremely helpful. If you have the resources to hire a coach, she will help you with your writing strategies—not writing content.