I use plastic. I've got three that I'm constantly washing so as to minimize the possibility of cross-contaminiation. They've held up pretty well over the years.
On a related note, at work we're experimenting with making signs out of Corian. We ordered a few 2 x 3 cutting boards and are putting vinyl letters on them. It's kinda cool.
Weber Smokey Joe
18" Weber Kettle
22" Weber clone kettle
Curb-foundling char-broil gasser
WSM: Assembled! First cook: 8/25/06
Fanatical devotion to the Q