Hardiplank or cement fiberboard is a less expensive green siding option to brick or stone, but just as durable.
The material is made from Portland cement mixed with ground sand, cellulose fiber, and other additives. This makes cement fiberboard more durable and less expensive than wood as well as being fire resistant. It's also impermeable to many common forms of damage that threaten wood siding, such as water damage, mold and rot. It will last for the life of the home and is very low maintenance.
For more information:
Read Mick Dalrymple's Ask A Pro Q&A, "Should I use fiber cement siding?"