Here are a couple of good chain guard options:
SKS Chainboard
I have SKS Chainboards on three of my bikes and I really like them. Light weight, easy to install, keeps my pants clean and unchewed.
Hebie Chainglider
Haven't tried the Hebie but it looks promising and there are some favorable reviews to be found on the net.
Civia chain guards can also be bought separately. Very attractive looking design.
B.