Hi,
I used Whizlabs for every exam i took (SCJP, SCWCD, and SCBCD). Each time I was satisfied with the simulator and the similarities with real exam. I got each time a mark for my "Final Exam" very close to the actual mark i got on the real thing.
Enthuware is good also, but I prefer Whizlabs.
About books, this is good, especially if you use Head First series books, but
you SHOULD use an exam simulator to train. Given the price of the real exam, it would be a shame to fail because you didn't buy a simulator....
Good luck to you all !