"Love... Think... Speak... Be walking trees. Be talking beasts. Be divine waters."

And you will be! Either stick to costuming as dryads, nyads, fauns, etc. or find some extreme creativity. Centaurs and Minotaurs could get interesting . . .

Narnia and the North: Aslan's Army ~
Tumnus
Warrior Fauns
Centaurs ~ male and female!
Red Dwarfs
Pauline Baynes's Dryads
Yet to come: Father Christmas, Film Dryads, Satyrs, Giant Rumblebuffin, Mermaids

The behind-the-scenes clips mentioned in some sections, the "Behind the Magic of WETA" and "Chapter II: The Director" featurettes, can be viewed at the official Narnia site. Most of the counter labels are given along with the images so you can look them up yourself, although this won't work if you're watching the streaming version.

Dryads - Basic Pauline Baynes Dryad
While we haven’t seen what the production dryads will look like, this is perhaps the most common and recognizable interpretation of the wood-nymphs: A very basic, Greek style with long ribbons or garlands. This is potentially a very easy costume to make!

Note: Made in other colors, these would make great nyad or maenad costumes as well. Tree-specific colors mentioned in the book are: "birch-girls in silver, beech-girls in fresh, transparent green, and the larch-girls in green so bright that it was almost yellow."

McCall’s 3514 Raised waist Greek/Roman costume, gathered at waist and bust line. V-neck front and back, with optional sleeves and one-shoulder variations.

Simplicity 9454 Simple, spaghetti-strap gown, gathered at neckline and belted under bust. Several cloak/over shirt variations.

Simplicity 5138 Dancing costumes. A lengthened version of view A or B would make a lovely dryad costume—perfect for the dancing lawn!