The main requirement of timber for timber bending is air-dried rather than kiln dried. In many timbers kiln drying sets the fibres to the point of being unchangeable. This is particularly true of Australian timbers. English/American timbers such as ash, elm, oak and beech all can be steamed and bent even after being dried to 10-12% moisture which is the normal content of imported timber. Timbers taken down to much lower moisture levels will have difficulty being bent.
Generally good bending timbers are strong. Unsatisfactory timbers are often soft celled and it is these cells that collapse when placed under the pressure of bending. Thus P.radiata and Western Red Cedar are unsuitable due to collapse causing heavy creasing on the inside face. Hardness is not a problem as Jarrah, Ironbark and Sugar Gum are all very hard timbers but all bend satisfactorily.
Be wary of using Vic Ash and Tas oak, primarily because of the mixed species that make up these composites. Unfortunately only some of each of the species bend while others do not and short of using a microscope the species are impossible to differentiate so it is a hit and miss proposition when using this timber. If you can be sure it is Mountain Ash or Alpine Ash then your bends will probably be successful, the other species not so successful.
Beech is a good bender but on thick pieces it can swell at variable and uncontrollable rates. I once did 6 window heads and ended up with thicknesses of 44 to 50, 5 were originally dressed to 45 and one was dressed to 44. The 44 was the only one that didn’t swell.
Blackwood, Celery-top, WA Karri, NZ Kahikatea, Spotted Gum are all proven benders but consider Silver and Black Wattle and street trees such as Grevillea robusta, plane tree, liquidamber and any of the ashes ( golden, desert, etc). Recently I have added sugar gum and ironbark to the range of timbers that we bend, oh and add Merbau to that list although only as a last resort.
If you are into bending and are experimenting for yourself try pallet timber. American pallets are often made of mixed species and are generally put together green so by the time you get one it will be sufficiently air dried. eg. engine pallets. Indonesia, Malaysia and Africa all provide interesting woods in pallets so look for pallets carrying inks and glass to name a few.