After a long search for a bitless solution to do dressage with I just found the LG bridle. It amazingly feels like riding with a bit, the horse understands just as well but without the pain, and reacts to the smallest wiggle of my finger. Compared to the Dr Cook, the release is immediate, which keeps the horse happy and soft. the bridle can be buckled in a few different ways for different effects, it even comes with the option of shanks for more control i.e. during trail rides. I am very very happy with it, and encourage you to try one yourself!
The bridle has been around for about ten years already, and is just now getting more known in the states. Here is the original website: http://www.lg-bridle.com/
and you can get it in the states from these stores: http://shop.nwnhc.com/
btw, I heard of a woman that rode with this bridle in a dressage competition. She had a paper from her vet stating that her horse can't have a bit in its mouth for medical reasons. The organizer accepted that without question, and the woman even won the competition!