Roz Kinstler (Lansing area). She's taken numerous people through the levels (to GP) and her students win everything. She was long listed for the Olympics, very active in USDF. Last year one of her Paralympic riders competed in the Paralympics in London. I don't recall what she placed. It wasn't top 3, but it was high. She also trains with a gentle, positive attitude.
Bernadette Radke (Grand Rapids/Kalamazoo area). She's taken several horses through GP. Her students clean up at shows. She's trained under Roz, Major Lindgreen (sp?) (I forgot the rest). Her students clean up at recognized shows, and none of them ride warmbloods (paints, QH's, TB's, Arab's, etc.). She's not fancy, but she explains things really well. Her style is more French classical.
Maryal Barnett (east Lansing). Has trained through GP. Is an FEI “C” Dressage Judge, an USEF “S” Dressage Judge. Her horse won "USDF Horse of the Year" award. I've taken clinics with her. I like her.
Sue Hughes (Northville MI). USEF r Dressage Judge and Centered Riding Instructor. I've clinic'd with her also. Great lady and knows her stuff. I've signed up for another clinic with her in Feb.
If you PM me, I can send you other recommendations but it'll take me some time to put it together.