When I took the test all the material came from their study guide. Some of the id stuff you can get elsewhere, just be sure to get the current ISA study guide. About $100.
The ISA study guide book has it all but I also found listening to the study guide in cd was helpful for me. It was kinda a subliminal method of learning without given me brain strain.
The CD ROM is a great resource, there is an audio CD set out there, would probably make me want to drive off the road into a pole though. The Richard Harris book, Arboriculture, An Integrated Management of Trees, Shrubs and Vines is great, also the Tree Climbers Guide by Sharon Lily. Team those with the above mentioned books and you should be good. The only tricky part would be ID.