x2
any reasonable hardwood is more than adequate unless you're trying to make some super skinny riser.
I think one guy made one from ERC, which is not strong by any measure of the word, it was just a little bulkier than usual.
alot of the common riser woods are ridiculously heavy and hard ... cocobolo is the perfect example ... that stuff is like a rock.
Wenge (hard and stiff but a little prone to cracking I think) doesn't seem to have interlocked grain at all.
maple .... obviously
hickory, oak, locust, osage, all the rosewoods liek kingwood, tulipwood, brazilian, etc ... shedua (personal favorite), redheart, ebony of all varities, purpleheart, ipe
basically anything other than softwoods and polar and I wouldn;t worry too much. When in doubt add phenolic I-beam!