Yes, you can use Repti-bark (sold for animal bedding and available at pet supply stores) or fine orchid bark. Or pretty much any other fine bark mulch of appropriate size - fir, spruce, hemlock, etc.

And here's a link to the search under this topic in the Container Gardening forum. Lots of posts under this topic and many quite recent!

Thanks for the help! I was searching in all of gardenweb, but I see now that most of the posts are in the container "forum". The reptibark is a much better price.