I'm planing to take the Adobe Photoshop ACE certification. I would like to know if is there any specific material and what is the recommended approach to study for the exam?
The Adobe [software] Classroom in a Book series from PeachPit Press will cover everything that could possibly be asked. YEs, its boring, dry, and hard to get through. But it's a lifesaver if there's an area of the app you don't use regularly.
The Prep guides are a good primer but not really detailed.
ExamAids.com has some decent practice exams. The questions aren't always close, and you shouldn't take the questions as being anything directly associated with the actual tests. Although, I understand the practice questions are, for the most part, written by those who have passed the tests. However, the style of questions are very similar and that's where the examaids can really be helpful.