I use newspaper, paper towel, or bath towels, depending on the size of enclosure and animal in it. If you are considering astro-turf I would strongly recommed just using bath towels. Much easier to keep clean since you can put it in a washing machine (IMHO astr-turf never gets fully clean). Towels come in the same colours, or any other colour you could possibly want
If you want something more natural looking I would recommend going with cypress mulch or carefresh (though its drabby grey appearance isn't very natural, still looks ok and can hold humidity, unlike aspen which molds quickly when dampened). Hardwood shavings are the only kind you can use, softwoods are all toxic, some are extremely mild [ex- fir (ie- repti-bark] so much that symptoms may go unoticed, but some like cedar which attack the neurosystem and can kill herps.