I use coconut bark, cypress mulch, and carefresh. not mixed together...of course!
some petstores had carefresh on sale for real cheap over the holidays so i stocked up on it. i used it mainly for my hamster, but i've started to use it for my king snake hatchlings, it works great.
and sometimes i can find coconut bark for cheap too...check out online reptile supply stores.
i can't use aspen...i have sinus issues and my gf has allergies. i tried, but as soon as i opened the bag, i'd have sneezing fits and i'd get all sinusey. i'd rather pay a bit more than deal with that.