Arco has a book called the Military Flight Aptitude Tests, they also have a guide called Mechanical Aptitude and Spatial Relations Guide and Learning Express has Military Flight Aptitude Tests.
I havent taken the test yet, give me a week and I'll be able to tell you which ones helped me the most.
Also, talk to your recruiter. He'll have a study guide and on top of that download the 3 gouges from this site. That should be more than enough material to go through.
I know I'll have trouble with the mechanical aspects and circuits since I haven't had anything like that since high school.
Good luck!