I generally use Johnson and Johnson baby shampoo. I was using a puppy shampoo for awhile, but then switched back to Johnson's because it's much more gentler and I'm not worried about getting it in his eyes accidentally when I wash his face.
I use Chlorhexiderm 2% shampoo on my Chi, Tucker. It is mildly microbacterial, and leaves the hair very soft and shiney. I bought it from my vet, though you can get it online.
A good way to clean your Chi's head is to put some shampoo lather on a cloth and wipe the face and outer ears, then use a cloth dampened in clear water to wipe the face. This way no water gets in the ears, and no soap gets in their eyes.
You can also put one drop of mineral oil in each eye before bathing and that will protect them from iritation from the shampoo.