Since WI legalized turkey dogs statewide this year I have been doing a lot of research on dogs. Jon Fries runs www.turkeydog.org
This is the home of the association Mark mentioned in his post. Jon was instrumental in getting dogs in WI legal and really knows his stuff providing a very informative website.
Basically most any breed including a mutt that has an interest in turkeys can be trained into a turkey dog.
My son living in OH has a golden retriever mixed with collie, one ugly dog but she can hunt turkeys. Last fall he took her out she flushed a flock of turkeys sat quietly next to him while he called the birds back using a wingbone call I made for him and shot his first fall turkey. He calls her a Gollie and apparently she is a natural turkey hunter.
Made my dog decision; I am picking up a Vizsla puppy on 2/2.
The Vizsla is one of the oldest hunting breeds originally from Hungary. Some contacts in KY use them for bird hunting and boar hunting. According to what I have read and been told these dogs can be trained to hunt multiple game and do it when the master instructs them. So I am giving them a try for turkeys. Hopefully he will be ready for this September turkey season.
Stay tune I am sure I will be posting pics and bragging about my turkey dog over in the WI section.