I passed the security+ in may,
I read the official sybex book, combined with my own interest in security. Basically the hardest questions I found where on the encryptions;
For example, it would list four and ask which was the most mathmatical strongest, then the next question would list the same four answers but ask which was the strongest to use. Both been different answers.
Im sure if you look at the braindumps around, where they offer to show you the first 10 for a demo, you'll see what I mean, of course I dont promote the use of these braindumps.